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Oil Paint Mediums 101
Modern oil paint mediums have come a long way since the time of Joseph Mallord William Turner, or J.M.W. Turner, (1775 – 1851) and Joshua Reynolds (1723 – 1792). Both of these painters, along with many others, used a medium, mixed with their oil paints, known then variously as Gumtion, McGuilpis, Macgilp and Megilp.
No matter what it was called, the formula was essentially a mixture of mastic varnish and an oil such as walnut, linseed, safflower or poppy oil, cooked with litharge or white lead.
Early oil paint mediums were a combination of oils, pigments and resins and took weeks, if not years, to fully dry. An artist could not add another layer of paint on top of a previous “un-dry” layer without the risk of the paint slowly dripping down the canvas.
Turner’s particular formulation of the medium megilp consisted of dried resin from mastic trees, lead acetate, linseed oil and turpentine. The resulting butter-colored, jellylike concoction enabled his oil layers to dry within days, ready for the next layer.
This allowed him to quickly build up luminous glazes of color giving his work a glowing appearance of sunlight.
Despite his famous carelessness about using fugitive reds in his paintings, it appears Turner was careful to formulate his megilp properly so it would not darken over time. The effect was sensational for the day and helped to make him famous.
Without megilp, it’s possible Turner may not have gained as much acclaim for his work. There is conjecture, however, that the detrimental changes seen in some of Reynold’s paintings may have resulted from his reliance on a less durable formulation of megilp.
Scientists have unraveled the chemical properties of Turner’s megilp to figure out why the mixture works. They have discovered the lead component of the mix generates a highly reactive form of oxygen.
This element reacts with the oils, speeding up their drying time. It also catalyzes the formation of an elastic organic-inorganic gel that holds pigments in place when additional paint layers are added.
Modern megilps, such as Gamblin’s Neo-Megilp, have been reformulated to get rid of the toxic lead, replacing it with a synthetic alkyd to achieve similar properties. The new version will not turn yellow or darken over time.
We use Neo-Megilp often and find it is a superb medium for creating transparencies in both direct painting and glazing. It is also our choice for turning a stiff oil paint into a buttery one without resorting to paint thinner, which breaks down the bonding qualities in paint.
Since Neo-Megilp dries more quickly than oil and adds elasticity to the paint film, it is an ideal substitute for oil when painting “fat over lean.” The added elasticity of the outer fat layers ensures the shrinkage of the drying under-layers will not crack the outer, drier paint film.
It is recommended to allow two to three days drying time between layers painted this way. We don’t always have the patience to follow that suggestion, so, like Turner, time will tell.
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And, if you want more insight on oil painting mediums, members can read the whole story in the article, “Understanding Oil Painting Mediums.”
— John and Ann