Pigments, Paints & Dyes

Today volumes and varieties of premixed paints are easily purchased in stores, but this has not always been the case.  Our predecessors just a generation or two prior had to make their own paints, whether intended for a house or barn, or for art.  Right up into the 1930’s or 40’s in construction, paint was made on the job-site and the contractors had to apprentice for many years before becoming competent and considered qualified to make quality paint.  The accomplished fine art painters or masters of yesteryear were akin to alchemist and their materials were varied.  Simultaneously however, many unskilled but ambitious artist may have watched their creations crack, change color or literally slide away from the canvas.  While premixed oil paints were being sold in little squeezable tubes by the 1860s, the knowledgeable and adept artist still depended upon the ability to grind his own pigments and mix his own paints.  With a little know-how it is actually easy to make a decent paint, in most any color.  Cro-Magnon cavemen mixed metallic oxides with tallow or clay to make paints that are still clinging to some stone walls today after thirty six thousand years have passed.  Our repertoire of pigments and binders has grown since then.  An attempt will be made here to organize and explain some basic binders, pigments and dyestuff.

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* Visiting cave paintings briefly;

   The elements are in a constant state of flux. The erosion and the degradation caused by mother nature is very rough. Any artistic medium must be robust to survive even a decade.  These cave paintings and sculptures of the long since past have only survived because they were sheltered and protected.  Most of the cave art in Europe created during the last ice age has probably been destroyed as a result of successive human activity.  Continued human habitation within a cave would lead to increased smoke and soot. Excessive carbon dioxide from both fire and human breathing might have encouraged detrimental lichen and mold growth upon the cave’s interior. Those caves today that still possess clear aurignacian or gravettian period cave art, do so because they became sealed off somehow from the outside atmosphere. The early humans that painted the pictures seldom if ever lived in those particular caves where cave art has survived. Multiple painters over a wide span of time created the artworks in these caves. Three of the most prominent caves in Europe still possessing pristine parietal paintings were just recently (analogous to their age) re-discovered. The Cave of Altamira in the north of Spain was found in 1879. The Lascaux Cave in the southern half of France was found shortly after the German occupation of France in 1940.  The Chauvet-Pont-d’Arc Cave of south France was re-discovered only in 1994.  These have all been sealed off again, as protection from outside atmosphere and from contamination by human tourism. Pablo Picasso who in 1948 visited the Lascaux cave before it was closed to the public, praised the prehistoric art; stating that man had learned nothing new since then.

The principle colored pigments used in the Lascaux cave for instance were the iron oxides or hydroxides known as hematite, goethite and ocher. Black pigments were provided by magnesium oxide and charcoal.  European cave paintings, engravings and sculptures are grouped together or classified as “Franco-Cantabrian” art because of their geographical concentration inland, both east and south of the Bay of Biscay.

Paint

It usually takes only two or three items to create a paint; a binder, a pigment and a filler.  Any particular paint is classified by its type of binder that in turn is reduce-able by a solvent.  Binders hold pigments and fillers together and onto surfaces.  Pigments can come from plants or animals, from dirt or rock minerals or they can be chemically synthetic.  Fillers if present might influence the opacity of a paint but mainly are added to expand or extend a paint’s bulk and coverage without affecting its color.  When comparing an oil, a tempera or an acrylic version of paint; these might all share the same exact pigment but differ only in having incompatible binders.  The chemical sophistication of modern day automobile paint mixtures are perhaps no more confusing, nor are more complex than some of the mixtures used on the pallets of the late Renaissance painters.  A host of toxic materials like arsenic, chromium, lead, radium and uranium were once commonly used in paints because they were effective.  Commercial house, furniture and spray paints today are usually less convoluted than the compounds once found on an artist’s pallet.  There, one may have found rarefied distillations of tree sap, rabbit skin glue, raw egg yoke, crushed up bug juice or perhaps even pulverized mummy remains.

Binders

The binder dries to form a film that then determines the texture, flexibility and permanency of paint.  Children like to taste things.  Naturally they put things in their mouths as they explore the world about them.  Many effective, once popular binders (or pigments as well) have been removed from commercial paints for this very reason.  Child safe paints, most of which can be produced at home anyway would include binders composed of glutinous grain starch (from rice, rye, wheat flours, etc), soap, shampoo, gum Arabic, shaving cream, gelatin, clay, honey and maple syrup.  Example paint binders not fit for consumption would include things like tallow, linseed and tung oil, shellac, raw egg yoke, beeswax, water glass (sodium silicate), acrylic, epoxy resin, alkyd resins and nitrocellulose lacquer.  A solvent is usually needed to thin out paint, to clean equipment or to clean up spills.  Some example solvents would include “the universal solvent” (water), alcohol, ether, essential oils, turpentines from plants, mineral spirits from coal tar, naphthas like benzene, toluene and xylene from petroleum.

   Casein is an ancient paint binder and glue, one regularly used by the Egyptians.  Made from milk protein, casein makes an excellent woodworking glue and it can also create a fine water soluble paint that dries quickly.  Used in ancient “tempera” (or preferably “distemper”) paints, casein paint was actually the favored medium for many modern illustrators right up into the 1960s. Then acrylic paints generally replaced casein bound paints in popularity, because casein paint if unused would tend to spoil after a few days.  For centuries moisture resistant casein glue has been used in laminated wood and furniture.  Casein immersed in formaldehyde created one of the earliest synthetic plastics.  Casein glue is milk protein (itself called “casein” which comprises about 3% of milk) dissolved in an aqueous alkaline solvent.  Making a simple casein glue or binder involves little more than causing milk to curdle by introducing vinegar perhaps, pressing out the excess whey and then neutralizing the acid with an alkali like sodium carbonate (baking soda).  Non-fat milk makes better glue than whole milk would because fat molecules prevent the casein from properly polymerizing.  Low-fat cottage cheese is already converted to curds so it works faster than milk.  The type of alkali used, substantially influences the properties of the final glue or binder.  Alkali s like borax (sodium tetraborate), ammonium carbonate (originally acquired by the destructive distillation of red deer antlers or “hartshorn”), potash (potassium carbonate) and lime ( either “quicklime” (calcium oxide) or “slacked lime” (calcium hydroxide)) have all been used to engineer casein glue and paint binders.  Quick lime or slacked lime works well for casein paints which need to be alkali resistant for applications like stuccoed walls or fences.  The “fresco” below was done by a Minoan painter sometime between 1600 and 1500 BC.

Fresco / https://commons.wikimedia.org/wiki/File:Fresco_of_a_fisherman,_Akrotiri,_Greece.jpg

Minoan Bronze Age fresco

When you mix cellulose with lye and heat it you get a mild but useful glue known as methyl cellulose.  Methyl cellulose can be used as a lubricant, an emulsifier, gel, as an additive for food, shampoo and toothpaste, as an additive to mortars and gypsum related construction materials and as a binder for medications, wallpaper paste, liquid paints and in dry pastel crayons.

  Hide glue and the gelatin we often eat in some processed foods are both made from an animal protein known as collagen.  It is soluble only in water and therefore is insoluble in oils, alcohol or other organic solvents.  Hide glue is typically made from animal hides and perhaps hooves, tendons and bones (that are cured in a lime slurry for a couple months before being boiled in water and then reduced).  The hide liquor can be further processed by drying and then by crushing it into chips, flakes or powders that are intended to be re-constituted with water at a later date.  A little heat is necessary so that the re-hydrated binder can be converted from a gel to a liquid before it is applied.  It does not store well in wet form and unused portions will mold.  Hide glue is the preferred glue used for stringed instruments like violins and cellos.  The wood in these delicate instruments is under stress and will expand or contract according to humidity, temperature or external pressure.  Hide glue when dry is appropriately flexible and weaker that the wood it is bonded to.  If a violin is stressed to the point of breakage then the glue bond should break before the wood does. Ideally the instrument can be easily fixed.  This is a handy feature considering that some 300 year old Guarneri del Jesu and Antonio Stradivari instruments can fetch more than $16 million at auction.

Usually animal skin glue is used to prepare, pre-coat or seal a ‘support’.  In the world of ‘fine art’ a support is the substructure of a painting – like wood, paper or stretched canvas.  The ground is the foundation, that first layer of primer painted upon the support.  The size is necessary only for fabric supports and it is painted on above the ground to plug up and and seal the canvas from the penetration of oils. Linen and cotton will prematurely rot without a size layer.  Many sizes have been used but rabbit skin glue was the most conventional ‘size’ used for oil painting and was supposed to be a bit stronger, more elastic and slower to gel than other hide glues.  If used for a ‘size’ then rabbit skin glue was usually mixed with gypsum, marble dust and titanium dioxide to create traditional white ‘gesso‘ sizing. Since climatic changes in temperature and humidity can cause old oil paintings to crack, poly vinyl acetate has become the preferred binder in contemporary ‘gesso’ or ‘size’ for fabric supports.  Fish glue or “isinglass” (made from air bladders, boiled skins and fish bones) was used by the ancient Egyptians and was later prevalent in the parchment manuscripts illustrated and gilded by medieval monks.  Fish glue was one of the more successful fixatives used in pastels, where pulverized pigment, white chalk and binder were commonly rolled up into a cylinder before they were dried.  Today isinglass is still useful as a “fining agent” for the clarification of some wines and beers.

* Tempera, Distemper, Encaustic and Fresco painting:

   Casein and hide glue have been used since antiquity to bind up and apply pulverized pigments.  The term “tempera” has often been used to casually imply several mediums (like egg, honey, plant gums milk casein and hide glue) though.  To most artist today “tempera” implies a technique employing only the egg yoke medium, and they might use the new term “distemper” to differentiate and encompass the other binders used in a similar way.  Tempera painting is very old and robust and was very common before “oil paints” became popular in the 15th century.  Some examples of tempera still exist, which were painted almost two thousand years ago.  Egg tempera dries very quickly so usually a bit of wine, vinegar or water is added to extend its period of workability.  Also about 2,000 years old, “encaustic” painting is a technique where pigments are added to melted beeswax.  Metal tools, special brushes and heat are used to spread the pigmented wax around before it solidifies.  “Fresco” (meaning fresh) is a technique where pigment is applied onto wet plaster.  The hue is drawn into and becomes part of the wet plaster itself after it is applied to ceilings, walls or murals. “Fresco-secco” on the other hand describes painting upon dried plaster.  The famous ceiling of the Sistine Chapel taken as a whole, is an enormous fresco painting done by Michelangelo about 500 years ago.

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  Silicate mineral paints are made from mineral pigments and soluble glass as the binder. “Water glass” (sodium or potassium silicate, liquid glass or Keimfarben) is made by melting silicon dioxide (silica / quartz sand) and soda ash (sodium carbonate) together.  The result is an exterior masonry paint binder or indoor product for mural painting, that is far more resistant to cold and damp and ultraviolet light than traditional lime fresco is.  Keimfarben was popular for a while as a 19th century variation of fresco, and remains useful today as a coverage for concrete and masonry walls.  Other uses for sodium silicate include its use as a paper glue in the manufacture of cardboard, as a tool for water treatment, as a fixative for reactive dyes, as a binder for refractory mixes and as a major component of dry-powder laundry and dishwasher detergents.

Oils

Some of the most important binders of all time are the so-called “drying oils”. These are the foundation of oil paints. When exposed to oxygen these particular oils have the property of polymerizing into the hard films we associate with dry finished, cured paint.  Linseed oil and tung oil are the most significant examples in this category but there are others less frequently used like poppy oil, soybean oil, castor oil, candelnut oil and so on.

  Linseed oil is squeezed from the seeds of the flax plant.  Flax seeds are edible and the fibers from the plant are probably the longest ones to be found in the textile industry.  Linen is the fabric made from flax fibers and both ancient Babylonians and ancient Egyptians cultivated the plant.  Raw linseed oil is edible but it does not dry or oxidize very quickly.  Therefore a quicker to dry “boiled linseed” was realized by experimentation.  In the 19th century additives like lead acetate and zinc sulfate were introduced to raw linseed oil and then heated, to improve the drying performance of the oil.  Today the heavy metal driers (perhaps cobalt & manganese salts) of boiled linseed oil may have changed to ones safer to handle, but boiled linseed is still not safe to eat.

  Tung oil (or Chinese wood oil) usage reaches way back before the Song Dynasty in China. The oil is squeezed from the nuts of a poisonous tree. This oil was or still is used for waterproofing wooden ships & paper umbrellas and for providing light when used as a lamp oil.  Modern day granite and marble counter-tops can be waterproofed and made stain resistant by thinned coats of tung oil.  Tung trees were once imported to the southeastern U.S. and planted as commercial crops.  Since that time the prolific and toxic trees have been classified as unwanted and invasive plants in states like Florida and Mississippi.  There have been incidents where school children on field trips have been poisoned after mistaking tung nuts for chestnuts.

Both linseed and tung oils make superior wood finishes that penetrate deep and rejuvenate cellulose.  Tung oil which is more expensive, may or may not be preferable in some situations because it is less likely to darken wood or to yellow.  Tung oil will eventually harden or polymerize by itself but boiled linseed preforms much faster – making linseed by far the most common drying oil employed in oil paints.

* Linoleum is a superior type of non slip floor covering made with linseed oil, which was invented around 1855 and became very popular by the beginning of the 20th century.  Being more flexible than ceramic tile, it could be applied to wooden floors and not crack under stress.  The thick inlaid linoleum floors were extremely durable but eventually thinner, printed pattern linoleum tile was manufactured.  Still this thinner linoleum flooring should be preferable to the cheap polyvinyl chloride (PVC) floor covering so popular today.  Simple enough to make at a remote construction site, linoleum fabrication usually began with a burlap or canvas backing.  The obligatory ingredients for linoleum tile were fine sawdust (or wood flour) linseed oil and some color pigment. Occasionally pine rosin and calcium carbonate (crushed limestone / as an extender) was thrown into the mix.  In fact, calcium carbonate (occasionally called whiting) is often used to extend or to fill in many types of paint, plastics and thermosetting resins.

Gums

Gums, resins, turpentines and essential oils come from plants and whether mixed to together or used separately they still have been used as paint binders for hundreds or even thousands of years. “Gums” for example result from “gummosis” which is a condition of sap flowing from a wound or disease in a bush or tree.  Gums are colloidal (a mixture in solution that does not settle) and are soluble in water while simultaneously being insoluble in alcohol or ether.  Resins may occur either alone or alongside gums and essential oils but they are conversely – insoluble in water but are dissolved by alcohol and ether.  Then there is a large group of harder resins called “copals”.   Amber which is a petrified tree sap, falls into this category.  Oleoresins are solutions of resin or wax mixed with essential oils and fatty oils.  Turpentine is an oleoresin collected and distilled usually from pine tree sap.  Balsams are like oleoresins but are generally more aromatic and occur naturally.  Essential oils are the fragrant, volatile compounds from plants, usually extracted by distillation.

Confusingly gum arabic and Arabic gum are two very separate but famous and important tree saps.  The natural gum and polysaccharide “gum arabic” comes from the hardened sap of select acacia trees.  “Arabic gum” (or mastic) on the other hand is resin collected from a totally unrelated dioecious shrub of the Pistacia (pistachio) family.  Both resins were known in antiquity, both were used in foods, as medicines, as paint binders and both still share great value as precious commodities.  A major portion of the world’s supply of gum Arabic comes from Sudan while most mastic comes from a small island, farther northwards from the equator.

Gum arabic is composed of saccharides and glycoproteins which give it the utility of a glue and paint binder and make it edible by humans.  Thousands of years ago the Egyptian Pharaohs were being mummified with the help of gum Arabic.  It is the same useful glue used on the back of a postage stamp, which is licked before sticking to an envelope.  It is used in cosmetics, shoe polish, candies and chocolates, to treat upset stomachs or to stop both diarrhea or constipation.  Gum arabic is indispensable in traditional lithography, paper and textile printing, where it controls viscosity in inks or repels ink from background areas on the plate of an offset press.  “A dab of gum arabic makes newspaper ink more cohesive and permanent”.   In medicine, gum arabic is used as an emulsifier to keep ingredients from separating or as a demulcent to temporarily defend the mouth, lips, tongue, eyes or nose from irritation.  It is used in glazes and paints, particularly in watercolors where it binds pigments to paper.  Gum arabic literally holds the multi-billion dollar soft drink industry together.  Without its ability as an emulsifier, the sugar in a ‘soda pop’ would crystallize and settle to the bottom of its container.  The economic importance of this tree sap has been influential enough to sway national policy.

Mastic or ‘Arabic gum’ was once worth its weight in gold.  It has long been collected from the sap of the Pistacia lentiscus shrub which is mostly cultivated on the Greek island of Chios.  Once dried in the sun the resin could be used as a chewing gum.  The English word “masticate” stems from an original Greek verb for chewing.  Mastic has antibacterial and anti-fungal properties that may counteract gingivitis and tooth decay.  Mastic also contains antioxidants and has traditional been used in medicine.  Just like the gum collected from Sudanese acacia trees, mastic is used to make cosmetics, incense, perfumes, soaps and lotions.  Transparent varnishes made with mastic were once very useful in preserving photographic negatives.

Resins

In the English language the term “resin” it too vague.  A resin usually denotes a highly viscous organic residue and a residue that often solidifies after contact with air.  Within the plant a resin might control water loss or act as an antiseptic. “Oleoresin” is a broad term for compounds collectively containing resins and oils (like turpentine).  At least two different types of oil are distinguished: fatty oils (containing fatty acid chains, lipids, triglycerides and such) and essential oils – which contain volatile aromatic compounds.  A “balsam” isn’t distilled but is an aromatic oleoresin that occurs naturally.  “Copal” was originally a semi hard tree sap used as incense by the natives of Central America, now it is a catchall phrase for similar resins that make good hard elastic varnishes.  Copals can be dissolved by oleoresins, by essential oils or by acetone; but to do so sometimes requires the application of heat.  Amber is a rock, a fossilized resin and the hardest copal.  Rosin is a resin usually collected from pine trees.  Rosin is what is left over after turpentine has been cooked and separated from pine tree sap.  After destructive distillation the leftover solid is ground up into a powder.   Rosin is used in adhesives, soaps, soldering flux, optical lens polishing compound, etching plates in printmaking and in oil paints and tempera emulsions of fine art.  It sees employment as a traction or friction enhancer used by rock climbers, weight lifters, bull riders, gymnast, ballet dancers, violinist and cellist alike.   There are many other plant gums or resins used as binders or glazes in paints.

Also found or even predominant in modern paints are thermosetting and thermoplastic resins.  A “thermoset” or thermosetting polymer is at first soft or liquid, malleable or mold-able before it is irreversibly cured or “set”.  Once hardened, heat cannot be used to change a thermoset’s shape.  Examples of thermosetting resin include Bakelite, epoxy resin, vulcanized rubber, polyurethanes and polyester resin and silicone (the rubber like adhesive and sealant, not the chemical element silicon).  Thermoplastic resins on the other hand are often formed to shapes by injection molding or extrusion molding, but once cooled are still quite modifiable in shape by the reintroduction of heat.  Example thermoplastics include acrylic, nylon, Teflon, polycarbonate, polyethylene, polypropylene, polyvinyl chloride and polystyrene resins.

*  Distillation is used to divide mixtures into separate components.  Destructive distillation (pyrolysis) uses heat to drive off valuable liquids and “volatiles” from organic material.  The organic material’s original form is lost, its molecules cracked, reduced or rearranged into new compounds.  Charcoal, methanol, tar and turpentine are gained by the destructive distillation of wood. Coal gas, coal tar, ammonia and coke are gained by the pyrolysis of coal.  Dry distillation is a case where gas is driven off from a heated solid and is then condensed and collected.  Mineral sulfates treated this way resulted in sulfuric acid when the gasses were absorbed by water.

*  Distillation of crude oil is preformed in an enormous type of still called a fractionating tower or column.  In such a tower the lightest and most volatile “fractions” are the first to rise to the top after the application of heat.  The liquefied petroleum gases such as butane, propane, propylene, butadiene, butylene, isobutylene are the first products to be removed and collected.  Next, in order of their vapor pressures; gasoline, naphtha, kerosene, diesel and fuel oil are separated.  An important phenomena occurring within such a column is “reflux”; an action where condensed vapors (liquid now) fall back down through the column, enriching rising vapors as they drop. 

Steam distillation is useful to extract many organic compounds that might otherwise be destroyed by the high temperatures in a normal retort still or reflux column.  With steam distillation, water vapor lifts vaporized particles from the mass and transports them to the condenser.  In effect the desired products are less damaged because distillation occurs at lower temperature.  Newer and more effective than steam distillation is vacuum distillation which lessens the pressure above the liquid mixture, effectively assisting in the quick evaporation of the lightest volatiles. 

Tiny amounts of essential oils can be extracted from plants by steam distillation or by solvent extraction.  Essential oils are the “essence” of a plant’s fragrance.  They are a concentration of ‘volatile aromatic compounds’ which are in effect only small molecules that change physical state from a liquid to a gas very quickly.  Volatile aromatic compounds move through the air quickly to stimulate the olfactory sensors in our noses.  Essential oils are used in medicines, foods, cosmetics, soaps, cleansers and perfumes.  They are frequently contained within oleoresins.

Lacquer, Shellac and Varnish

In general, lacquers are differentiated from paints by virtue of being more glossy.  The word “lacquer” is derived from the lac insect and a Sanskrit word for the number 100,000.   Millions of these little insects are cultivated for the purpose of secreting a resin that they produce after sucking sap from a tree.  “Shellac” (mostly coming from India) is the filtered and refined bug resin that makes such a useful wood finish and dye for both fabrics and leathers.  There is also a long established lacquer in the orient which is extracted from the Chinese or Japanese “lacquer tree” (Toxicodendron vernicifluum).  This tree sap which turns into a strong safe clear film once dried, actually contains the same poisonous irritant as “poison ivy” and therefore is difficult to work with when wet.

One or two centuries ago westerners tried to imitate the effect of Oriental shellacs and lacquers with what are called “varnishes”.  Omitting synthetic alkyd and polyurethane examples, the best (natural) varnishes came from dissolved copal resins.  Varnishes can be categorized by the type of solvent used.  ‘Spirit varnishes‘ for instance usually use alcohol as the solvent, but occasionally employ naphthas (the lighter liquid petroleum fractions) also.  Certain resins when mixed with these solvents dry fast and hard.  The film may stay clear (does not yellow with age) but the “spirit varnish film” is thin and brittle and not very durable.  ‘Essential oil varnishes‘ will use a heavier solvent like turpentine mixed in with the resin.  While this makes a tougher film than spirit varnish, it may take a long time for the solvent to dry.  Finally the ‘fixed-oil varnish‘ employs a resin mixed in with a “drying oil” like linseed oil. This makes the toughest, thickest most durable film or varnish of all.

   Latex paints might use water soluble acrylic resin, vinyl acrylic or styrene acrylic as binders.  White glue (like Elmer’s ® glue) that children soon become familiar with is actually polyvinyl acetate (PVA or “caparol”) and has the same composition as cheap latex paint.  There is no real latex in ‘latex paint’ actually.  “Latex” should denote natural rubber extracted from a jungle tree, not a synthetic polymer.  Acrylic resin, vinyl acrylic (PVA) and styrene acrylic bound paints are erroneously called latex in the U.S., but their called “emulsion paints” in the UK.  Their chemical composition is complex and far beyond the capability of the average person to replicate.

*  Acrylic resin is about twice as expensive as vinyl or styrenated acrylic.  A typical interior ‘latex paint’ contains about 20% acrylic and 80% vinyl.  Latex paints were unknown before the 1930’s or 40’s.  Prior to that time exterior paints were often made with linseed oil binder and interior paints were often based on milk (casein).  Today’s interior latex should be considered superior in most every way to yesterday’s casein or milk paints.  Exterior latex may exhibit good durability and fade and crack resistance but has not yet completely displaced old fashioned oils.  Here linseed based or alkyd based oil paints are extremely durable themselves and unlike acrylics will often penetrate deeper below the surfaces of wood and rust.  Exterior latex with 100% acrylic binders preform very well though in terms of UV resistance and in alkali resistance when applied to concrete & masonry.  Cheaper, predominately vinyl acrylic latex does well inside where smudges and grime may need to be scrubbed from walls.  Styrenated acrylic latex paint is often used on ceilings; its also good as a concrete or masonry sealer because it resist alkali burn and efflorescence (that situation where salt leaches through to the surface of concrete or another porous material and forms crystals).

   Alkyd paints were invented in the 1920’s, improved upon and used sporadically by some in the 1930’s and were commercialized in the 1940’s.  DuPont produced its first alkyd paints for artist in 1931.  The word “alkyd” (or “alcid”) is derived from the words “alcohol” & “acids”, which are both required to make the polyester.   Alkyds are polyesters manufactured from polyols (alcohols), aromatic acids and organic fatty acids.  Alkyds have become the most common “oil-based” type, premixed paints that are commercially available.  Since alkyds are made from both petroleum and vegetable products they are also reduced or thinned by most petroleum solvents or vegetable oils.

   Epoxy polymers are mixed with complimentary hardeners to produce whats called a thermosetting resin.  A thermoset is at first wet or soft before it becomes hard, insoluble and irreversibly cured.  Thermoplastic polymers on the other hand are pressed or injected into molds using heat.  Epoxy resins are important engineering or structural adhesives but they are more frequently being used as tough paint coatings by industry as well.  The surface paint or a priming undercoat of an automobile may be epoxy resin because of the superior adhesion and corrosion resistance this paint provides for metal.  Many water pipes, rebar (iron bars used to reinforce concrete), appliances like refrigerators, stoves, laundry driers and washers are covered with epoxy powder coat called FBE (Fusion Bonded Epoxy Powder Coatings).  Epoxy coatings are more heat resistant than latex-based or alkyd-based paints but they still deteriorate under UV exposure.  Like both latex and alkyds, epoxy resin was thought up and perfected by chemist rather recently (the 1930s).

  Nitrocellulose lacquer:  Many women paint their fingernails with the same chemical used to make gunpowder.  General Motors began painting automobiles with the lacquer in the 1920’s.  Nitrocellulose (guncotton or collodion or cellulose nitrate) was not the first “high explosive” because “nitrostarch” was discovered or invented about thirteen years before.  The inventions of nirtoglycerin and then dynamite would follow, not precede guncotton.  In 1846 nitrocellulose was apparently discovered or stumbled upon simultaneously by three different chemist working concurrently in separate laboratories.  It was made by saturating plant cellulose (like cotton) in nitric acid.  Nitrocellulose became the main ingredient in smokeless gunpowder and it became a support for photographic film.  It was probably the first plastic, and as a substitute for ivory it was soon molded into piano keys, billiard balls, tool handles and so on.  Nitrocellulose was also used to make the first transparent plastic roll film used for photography and it was used as a binder for tough, glossy automotive paints.

* Before nitrocellulose, nail polish might have been made from a mixture of gum Arabic, beeswax, egg white, gelatin and vegetable dye.

* The most common nail polish remover is acetone but his can be harsh on skin and nails. Sometimes ethyl acetate is preferred and this us usually the original solvent for nail polish itself, anyway.

* Before Henry Ford started making millions of his Model T’s, the other car makers used oil paints to accent their automobiles. As early as 1865 commercial oil paints began to appear that had extended shelf life due to the addition of sodium silicate (see waterglass or Keimfarben above). Based on slow drying linseed or tung oils these other car paints might have taken several weeks to harden. These oil based paints looked good for a year or two until ultraviolet light from the sun began to fade, yellow or dull the color. Ford’s innovation was to develop asphalt-based baked enamels for his cars that were similar to a paint technique called “Japanning”. Japanning is a dark decorative patina or finish acquired by painting a thin layer of bitumen (asphaltum) over an object but allowing some of the original surface to show through. Ford saturated his fenders, hoods and other metal parts with Japan Black (a paint bitumen) suspended in linseed oil and tinned with either mineral spirits or petroleum naphtha. The wooden components used a different paint recipe. Then as Japanned ornaments usually are, the metallic parts were baked in a tunnel oven for about an hour on a separate, slow moving assembly line. At the height of production a new Model T – with paint thoroughly dried – rolled off the floor about every three minutes. Drying time was not the only consideration for Ford, because the black paint job was much cheaper and ultimately more durable than what the competition was producing.

* Pierre DuPont owned stock in General Motors, years before his chemical company developed nitrocellulose paint lacquers. Around 1923 GM hit the automobile market with cars painted in new colorful “Duco paints” (pyroxylin / nitrocellulose based). These paints came in every color of the rainbow and took only minutes to dry. In the 1930’s the first metallic car paints appeared. These used real fish scales at first and eventually graduated to cheaper aluminum flakes. Sunlight resistant clear coat enamels for cars appeared in the 1940’s. The first synthetic polymer / transparent thermoplastic, “acrylic resin” car coats appeared in the 1950’s. These had the advantage of drying much faster than enamel coats. Acrylic lacquers were eventually superseded by what is preferred today, which is usually called a “clear coat finish”. A clear-coat-finish usually consist of a primer, a color coat and a clear, tough, polyurethane topcoat.

Fillers

Fillers are intended to increase and extend the coverage of paint. Fillers are cheap, non-essential components that add bulk and might sometimes influence opacity. Example fillers include: clay, chalk, powdered marble / calcium carbonate, mica, baking soda, plaster of Paris, tile grout, sugar and vinyls like polyvinyl chloride or polyvinyl acetate.

Pigments

Practically any attractively colored earth can be used for homemade pigment.  A good way to process it is to boil a quantity in water for several hours.  Strain out the impurities and larger aggregate and pour off the excess water.  Place the still moist residue in shallow pans and allow to dry.  Grind further in mortar and pestle if possible and sift once more through a finer screen or filter.

Pigments are insoluble color particles that require a binding agent to hold them onto the surface of the material being covered.  The first pigments came from the earth and from inorganic metal oxides.  This limited and somewhat dull spectrum or pallet of colors was eventually broadened and enhanced during the early 19th century.  Some new colors were created then, when mixtures of metal oxides and earth pigments were cooked and fused together under high heat.  Finally, by the end of the 19th century, advancements in a new field of science known as organic chemistry enabled the creation of several intensely vibrant colors.  Modern synthetic pigments, inks and dyes are based upon the carbon molecule and were created in laboratories.  Today almost every natural pigment has been replaced by a synthetic organic alternative.  Modern pigments behave differently, not necessarily better than older mineral pigments in that when mixed or thinned down they generally shift in “value” and not in “chroma”.

https://commons.wikimedia.org/wiki/File:Munsell-system.svg This image © 2007, Jacob Rus

Some common earth pigments include green earth, goethite, ocher, hematite, sienna and umber.  Some natural mineral pigments include Malachite, Vermillion and Lapis Lazuli.  Some artificial mineral pigments not found in nature are Venetian Red and Caput Mortuum.   Some organic pigments of natural origin would include carmine, gamboge, Indian Yellow, madder root and mummy brown.  Some synthetic inorganic pigments that are manufactured include Ceruleum blue, Prussian blue and Cobalt blue, Cadmiums and White Lead.  Some synthetic organic pigments (lab created / carbon based) include the azo pigmens, dioxazine, isoindolinones, quinacridones and phtalocyanines.  There are too many pigments with too many details to define them all properly here.  Entire books have been dedicated to the subject. The vast majority of pigments available in the marketplace today are actually synthetic.   A short, far from complete list of traditional, non synthetic paint pigments follows.

Green Earth is similar to ocher; a mixture of ferrous hydroxide and silicic acid.
Goethite (Brown Ocher) is a unique mixture of ferrous hydroxide.
Ocher (usually a yellow) is a clay that contains hydrated hematite (an ore from which iron has been smelted for the last 6,000 years).
Hematite (usually red unhydrated mineral iron ore) stems from a Greek word for blood. “Limonite” ore comes from the Greek for meadow (meadow/ marsh/ bog ore/ brown / yellow). Ocher then is a catchall phrase for abundant natural earth pigments containing iron oxide and depending upon hydration states and additional ingredients may range in color between yellow, red, purple and brown. The artist and painters of the Medieval and Renaissance period knew how to cook ‘ochers’ with heat to drive away the chemically bound water, achieving unique hues.
Sienna (usually brown) is a mixture of iron oxide and manganese oxide. Yellowish-brown “raw sienna” is turned into a reddish-brown “burnt sienna” when cooked with heat.
Umber (both raw and burnt) is also a mixture of iron hydroxide and manganese oxide. It is usually darker than either ocher or sienna.
Malachite (usually green) is a hard copper carbonate mineral. It often comes from underground stalactites. <pic>
Ultramarine (deep blue) was originally made from crushed Lapis Lazuli. It was an extremely expensive pigment that was hard to make and it was used sparingly. <pic>
Venetian Red pigment comes from red iron oxide but it is artificial because it is or was collected from heated chemical waste of manufacture.
Caput Mortuum (usually purple) from Latin – meaning “worthless remains” was usually collected from leftover, useless iron sulfate (copperas) residues.
Carmine pigment (crimson or bright-red) is obtained from carminic acid.  Since carminic acid wasn’t reproducible in the laboratory until 1991, it has since ancient times been acquired by crushing up little scale insects.  Polish cochineal and Kermes dyes were both from scale insects and known in ancient Europe and were later valuable commodities in the Middle Ages.  Mexican or Spanish cochineal (from a different, New World scale insect that eats prickly pear cactus) quickly became the preeminent scarlet dye in the 16th century.  Although carmine or cochineal are better known as food colors, lipstick and fabric dyes today, artist like Michelangelo also used them in paints.
Madder root has been used since antiquity as a (red) dyestuff, but it has also been used for tinting paints. It wasn’t known in Europe until returning Crusaders brought it back to Italy. During the Colonial Period the typical red uniform of the British Army was dyed with madder root, while the officers that could afford it had their own uniforms tailored and dyed with brighter and more colorfast carmine or cochineal dye.
Gamboge is a saffron / mustard yellow pigment that is obtained from the sap or resin of a tree. It is the traditional color and dye used for the robes of certain Buddhist monks. It is often used in watercolor but is not lightproof.
Indian Yellow is was collected from the urine of cows that ate mostly mango leaves. It is a natural organic “lake” pigment. Authentic Indian Yellow is quite permanent, very expensive and often imitated.

Uranium Yellow from uranium oxide; often found in vanadium ore, made a useful pigment before the Manhattan Project found a better use for every available bit of the element in the 1940’s.
Orpiment (yellow) and Realgar (red) were both popular since Roman times as pigments.  The two pigments differ slightly in chemical composition but both consist of poisonous arsenic sulfide.  Arrow tips were occasionally dipped into solutions of these minerals to make them more deadly.  The minerals were originally found as crystalline deposits nearby volcanic fumaroles and geothermal hot springs.
Vermillion (bright red or scarlet) comes from the crushed crystal of mercury sulfide known as “cinnabar”.
Emerald Green was a very poisonous and dangerous pigment made from copper arsenate. By itself it made a durable and attractive pigment but would later turn black if mixed with sulfur colors (like cadmium yellow, vermilion and ultramarine).
Mummy Brown was a very useful and popular paint pigment made from the crushed up remains of Egyptian mummies. Most artist in the past did not know of its true origin. Perhaps some pigment called mummy brown was produced by burning ‘green earth’. Mummy Brown was still being made in the 20th century until sources of available mummies finally ran dry.
Asphaltum or bitumen is a brown / black pigment derived from solidified petroleum. It might be used as a binder for gravel and sand in asphalt road surfaces but it has also been used as a pigment. Ancient aboriginal N. American Indians used it to decorate pottery and Henry Ford used it to paint automobiles.
Ceruleum Blue; a synthetic inorganic pigment made from copper and oxides of cobalt
Prussian Blue (also Paris Blue or ferric ferrocyanide) was the first modern synthetic pigment. It is a dark blue, non poisonous, iron-cyanide based compound with intense chromatic power. It was the main color of uniforms used in the Prussian Army and was the traditional blue used in “blueprints” (or cyanotypes – which exploited the light sensitivity of paper perhaps, coated with gum Arabic & ferro-gallate (acidified iron) type solutions).
Cobalt Blue is made from heating together cobalt and aluminum oxide. Some Chinese porcelain pottery has mixed the same minerals for many centuries but blue glass and cobalt blue paints have been used now for about 200 years.
Cadmiums are very vibrant and light-fast yellow, orange and red pigments made from oxides of cadmium. They are expensive pigments, potentially toxic and superior to modern organic alternatives in almost every respect. <link Europe ban>
White Lead (or Cremnitz White) is lead carbonate and has historically been the principal white pigment of classical European oil painting. When mixed with a dryable oil it spreads wide and covers especially well and with high opacity. White lead paint was once commonly used to protect the hulls of wooden ships from shipworm. Unfortunately lead paint has been banned in most countries because of its potential toxicity and ‘titanium white’ has replaced it. Lead carbonate is the same substance that forms white crystals on terminals of a car’s battery. Historically the pigment was produced by subjecting lead to the fumes of strong acetic acid <vinegar>. Red Lead paint on the other hand is lead oxide and was once very valuable as an anti-corrosion / rustproof primer paint. For example this primer distinguished and protected the Golden Gate Bridge near San Francisco for thirty years before re-painting became necessary and before the formula was changed.
Titanium White is titanium dioxide (Ti O2) and is non poisonous. It has great covering power and is bright – with a high refractive index.
Zinc White is zinc oxide. It is a very useful non toxic pigment developed about 170 years ago that tints less or is more transparent than titanium white.
Zinc Chromate when used as a pigment was known as Zinc Yellow.  It is not used in art anymore because it degrades quickly to brown and is toxic and carcinogenic.  Zinc chromate does make a very useful paint coating in industry where it is used to passivate (protect from corrosion) metals like tin alloy, galvanized steel, cadmium, magnesium and aluminum Metal tools that have undergone a chromate conversion coating usually display a distinctive yellow-green iridescence.

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Dyes

Again, the difference between a pigment and a dye is that one is soluble and the other is not.  Inks incidentally, can be either dye-based or pigment based solutions.  Paints need a binder to hold little solid particles of color pigment to a surface.  Dyes on the other hand contain infinitesimal refractive coloring compounds that are dissolved in solution.  Pigments are generally better than dyes in keeping their color by resisting damage from high heat, bright light or chemicals.  Dyes can cling to or be absorbed into only a few types of surfaces.  Without special preparations, dyes cannot be turned into the pigments used to color paints.  Therefore a “laked pigment” is one wherein a soluble dye is absorbed by or chemically bonded to a transparent insoluble salt; which then leaves behind a particle of insoluble pigment.  Calcium salts from sources like bones, chalk or white clay were historically the first salts used to entrap dyes for use as pigment.  Today chromium and cobalt metallic salts are more frequently used to manufacture lake pigments.

From ancient times people have been dyeing fabrics and leathers and furs.  Woad, weld and madder are natural dyes that have been used for the last 3,000 years or more.  Today dye chemist are busy designing ever better molecular dyes, for the examination of neurons in a nervous system or to study DNA by examining specific genes.  Other dye chemist might be busy perfecting a contrast dye for use by an MRI (Magnetic Resonance Imaging) machine or inkjet solutions for 3D printing or microcircuitry fabrication.  Here they would need to consider electrostatic properties, solvent compatibility, resistance to bleeding and spreading, consistency and flow properties or perhaps the adhesion of dye or ink to a substrate.

Wool and other so-called “protein fibers” like hair and silk are the easiest fabrics to color with a natural dye.  First the oils on fibers like wool need to be washed or “scoured” away before a dye can penetrate.  Cellulose fibers like cotton, linen, flax, hemp, jute, paper, cane, rattan, etc. are less suited to natural dye uptake and may need to be treated beforehand by a mordant.  A mordant is a chemical used in solution that helps embed color into a fiber.  Taken from a French word that means “to bite” or to take hold, a mordant allows the penetration of a dye into fiber,  similar to the way a laked pigment binds within a crystal.  Some “substantive” or “direct” natural dyes like those from walnut hulls, Tyrian purple from a sea snail, lichens, onion skins, tea or coffee will stain and stick to wool without the help of a mordant, but these might eventually wash out or fade.  Substantive or direct dyes without assistance of a mordant cling to fibers by relatively weak hydrogen bonding.  Other types of dye molecules however can attach to fiber molecules by complicated Van der Waals forces or by ionic or convalent bonding.  The most permanent dyes are fiber reactive dyes that establish strong covalent bonds.

The most common mordants are alum, copper sulfate, chrome, iron sulfate, tannic acid and tin.  Some of the direct dyes already contain a tannic acid mordant (ex: walnut, oak and pecan husk, tea & coffee).  The choice of mordant will usually influence the outcome of the dyed color.  Alum (aluminum potassium sulfate) causes the least change in color.  Copper sulfate (Blue vitriol) sometimes turns fibers green.  It can be collected by soaking dirty old pennys in acid.  Iron sulfate (copperas) “saddens” color and makes them more green-brown or gray.  Historical “iron gall ink” employed iron sulfate.  Copperas can be made by soaking rusty nails in sulfuric acid.  Tin (stannous chloride, specifically) brightens colors, especially reds and yellows, but it can be very harsh on fabrics.

To bring this complicated topic to a shortened end so that this blog post can be published today rather than next month; many details about dyeing will need to be skipped for now.  The goal at present is to explore dyes insofar as they intersect with pigments and paints.  Perhaps this segment on dyes will be amended later.  More time is needed to compress information and to insert little details.  For instance, for forty years following its invention TNT was used only as a yellow dye.  TNT is so insensitive it took that long to find a satisfactory way detonate it.  Poke berries are not commonly used for either dye or ink; but the final draft of the American Declaration of Independence was penned in fermented poke berry juice.

Paint recipes

The Internet is loaded with recipes for children’s paints.  These may contain binders of soap, glue or flour and pigments of Kool Aid ® or food coloring and the like.  One may find a recipe for creating a paint from egg yokes and colored chalk.  { Michelangelo may have used the same tempera ingredients on the Sistine Chapel but since he painted upon wet plaster the work is called fresco, remember }.  Digging deeper one can find recipes more applicable for bulk paints.  There is no need to replicate here, the work already done on another web site.  One decent site providing information for homemade paint is provided by motherearthliving.com.  The following list of ingredients for “Clay paint” is copy and pasted here, as insurance against the possibility of “link rot” in the future.  The paint’s final color would be determined by both the hue of the powdered clay chosen and by any auxiliary pigments added.

CLAY PAINT
1 part wheat, rice, rye, or potato flour
2 parts cold water
1-1/2 parts boiling water
1 part powdered clay
1/2 part inert powder filler (options: mica flakes and powder, chalk, powdered ­marble or silica, 60- to 80-grit sand for rougher surfaces)

Gritty “chalkboard paints” similar in texture and performance to the slate chalkboards found in old school rooms can be created from either commercial latex (emulsion) paints or homemade paints.  One simply adds plaster of Paris, baking soda, un-sanded tile grout or calcium carbonate to the paint.

A simple black paint can be made from potatoes.   Several potatoes are slowly baked in a fire or in an oven until they turn completely black and dry inside.  These are then crushed to a fine consistency and the powder is mixed with linseed oil.  For a useful olive drab (Army green) color one can add yellow ocher pigment.

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