How Linseed Oil has been used as a binder in European Painting History
PAINT -- pigment bound in oil, was found among the art materials used to create 8th century CE wall paintings in the caves behind the colossal Bamiyan buddhas that were destroyed by the Taliban in 2001.
Indications are the paintings were made using glazing techniques. In the caves, scientists also identified natural resin varnishes, hide glues and wax, all ingredients of the pre-Industrial Revolution oil painting system found in every studio. Because the pre-Industrial Revolution period is about 40,000 years, finding materials used for millennia in alchemy, medicine and painting along the silk road does not seem surprising.
What surprises me is that anybody still thinks oil painting erupted fully formed from the knee of the Renaissance. Oil painting is a revolution in technique not an innovation in materials.
Recent discoveries in the Afghani caves demonstrate again how artists used oil painting techniques before their “invention” by the Van Eycks et. al. The brothers were among the earliest Netherlandish painters to recognize the ideas that matched the materials, mastered glazing and painting wet-into-wet.
They mastered those techniques because they chose slow drying linseed oil as their primary paint binder instead of quick drying tempera. Look at an egg yoke, you can’t see through it. Look at a glass bottle of vegetable oil, you can see through it. If you want to make more transparent paint, take out egg yoke and add linseed oil.
WHY CHANGE THE BINDER?
Before the 15th century CE, fresco, mosaic and tempera were the three media that dominated art making. All three media make matte, flat opaque surfaces.
Obviously, that’s the look customers wanted. A mixture of pigment with a water soluble binder, tempera holds a fine line, and sets to durable surface that requires varnishing only to increase sheen.
Maybe after a thousand years the matte, flat look was simply passé.
Or, maybe, a new knowledge emerged about how single point perspective can be used to create a sense of depth on a 2D surface.
By using a transparent binder to slow down the trajectory of light waves as they penetrate through the layers, painters can make paintings glow. As light waves struggles out of the painting, they leave behind enough energy to make layers alight. Layer upon light filled layer makes deep, luminous surfaces.
Seeing single-point perspective must have been the eureka moment for Florentine architect Filippo Brunelleschi (1377 – 1446). He used mathematics to redefine Gothic sense of space and to establish a new view of perspective and symmetry.
His new view must have inspired painters. However, they needed a transparent binder to paint how the world looks in 3D. They went to their studios and linseed oil was already there.
Among other oils such as poppy and walnut, heat-bodied or cold-pressed linseed oil would have been preferred in painting because of dry rate.
Linseed is the oilseed of the flax plant, among the first cultivated crops, grown for fabric, lamp oil and culinary oil. The human body cannot produce two key fatty acids, linoleic and alpha-linolenic (unsaturated omega-6 fatty acids), which are widely available in plant seed oils.
Linseed oil has the highest linoleic and alpha-linolenic content among oil seeds.
Only one species of flax, Linum usitatissimum, has been continuously cultivated for both fiber and seed continuously for thousands of years. Taller, willowy-stocked flax stems are harvested just after first flowering and processed into linen fiber. Sturdier, lower growing flax plants flower fully then their seeds are processed into linseed oil.
Linseed oil is the only naturally occurring vegetable oil that hardens when exposed to air. During oxidation (drying) process linseed oil has a strong odor and a short shelf life.
Its tendency to thicken and stink made other oils preferable for culinary and medicinalpurposes. Its true value has always been its tendency to thicken. When boiled with tree resins like frankincense and myrrh, linseed oil makes an oil varnish so tough it makes boats float.
Common to all boat building cultures, the oil varnish technology may be older than Ethiopia, which still cultivates flax. Source of 85% of the Nile River flow, perhaps Ethiopia is source for oil varnish used in Egypt since the Old Kingdom. An ancient name for Egypt is “land of flax.” “Linon” is Greek for flax.
Throughout the expansion of boat building cultures and world exploration by ship, demand for linseed oil made it commonly available, inexpensive and usually unadulterated with anything other than camelina oil and weed seed oil. Camelina, a slow drying oil seed crop, was historically planted with flax to discourage weeds. Weed seed oil is non-drying. When too many weed seeds are crushed with flax seeds, weed seed oil contaminates linseed oil and inhibits its drying into a hard film. For industrial varnishes, lower quality oil was boiled with hard tree resins and metal salts into a thick chocolate brown.
Alchemists and painters would have cultivated suppliers who delivered very light colored, quality oil.
Linseed oil would have been purchased by the gallon equiv. Reasonably, professional painting studios purchased linseed oil at the best price for a high volume that would last for a few years. Consider two gallons makes hundreds of tubes (equiv.) of paints.
Cold pressed linseed oil (CPLO) was the obvious choice but expensive because culinary/medicinal oils are more expensive than industrial oils.
As a colormaker, I probably would have done then what I did 20 years ago when I bought CPLO batches that did not meet food grade standards from an organic processor. But I did not chose to make artists’ paints from CPLO because it yellows too much. I preferred refined linseed oil because it has better color, is widely available and much more reasonably priced. Refining removes some of the oil’s drying power and the fact is balanced by purity and light color of modern refined linseed oil.
Whether prepared in studio or purchased, I prefer low temperature heat-bodied oil because I think it makes better paint. The reason to heat linseed oil is to improve its uptake of pigment, improve dry time and reduce odor. Over the course of a few years, oil improves in storage. The mucilage and other debris drop down. As the drying oil continued to form long chains, its working properties move from oily to buttery.
Above 150 degrees F., the oil starts to move. About 225 degrees F., linseed oil starts polymerizing and long chains quicken the liquid. At this temperature, enough oil would have been removed for painting studios on contract. The oil would be cooled down, sealed and stored away from light and air.
The process of refining linseed oil took all day. There was a mention in an old recipe book about adding an onion and small loaf of bread to the hot oil. When I first heard that, I wondered if it was to defat the oil somehow but now I think the worker’s lunch was fried onion and bread.
To the remaining oil, more fuel was be added until the temperature reached a point at which the linseed oil thickens into stand oil and plate oil. By the 16th century, printers demanded high quality fast drying inks made from highly polymerized oil.
More fuel was added very carefully. Linseed oil explodes at 548 degrees F.
Making oil varnishes was the last, most dangerous step of oil processing.
The oil started to roil. Suddenly, the temperature intensified until the oil boiled over. Fire reached up and ignited gallons of linseed oil into a flaming grease ball that nearly burned down friends’ vineyard!
After more than six hours spent watching oil slowly thicken, losing control of it took about a minute. I understood why making oil varnish and printer’s ink were called “black arts.”
Not only do they make black products, cooking linseed oil probably burned down whole towns!