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Literally Watching Paint Dry

Post #1846 • September 16, 2019, 11:29 AM

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On September 7, I mulled four piles of paint, two parts ultramarine pigment to one part of oil. I regard that as a soupy paint, but it had enough bulk not to drip. The first pile entailed a quality store-bought linseed oil, namely Gamblin. The other three oils I refined by hand, using vodka, psyllium husks, and salt water respectively. (I had shaken the vodka batch with chalk to condition it further. This ended up mattering.) I then drew down the piles with a palette knife on a cheap canvas, creating a transition that went from impasto to scraping with an intermediate thickness along the way comparable to a loaded brushstroke. I will refer to these batches and the recipes that produced them as Store, Vodka, Psyllium, and Salt hereafter.

After two days, much of the gloss had come off of the scraped portions of Vodka and Psyllium. Vodka was already tacky, while Psyllium was wet but hardening up. Salt had turned semi-gloss and was beginning to get sticky as well. Store was as wet and shiny as the day it was put down.

Come Day 3, the scraped portions of Vodka and Psyllium had dried to the touch. (Dry here and from here on only means "feels dry," not "insoluble on contact with another layer of wet oil," which is going to depend on individual handling, and certainly not "at a state of minimum energy," which can require months or years in an oil painting. Caveat lector.) The brushstroke-thick areas of their drawdowns had become tacky. Comparable areas of Salt and Store lifted when similarly poked. Salt lost a little more gloss, while Store maintained its reflective sheen.

On Day 4, scraped portions of Store and Salt had finally dried, and their brushstroke-thick areas felt tacky, though they lifted easily. Brushstroke-thick areas of Psyllium had hardened even further but not to solidity. Almost-brushstroke-thick areas of Vodka felt dry.

By Day 6, a curious thing had happened. Brushstroke-thick areas of Vodka and Psyllium had dried to an attractive gloss. Conversely, Salt had lost its gloss but hadn't dried much further at all. The effect didn't last - the final results were of identical gloss for all the oils. But in my salt refinement post, I made fun of Eastlake for thinking that oil required the addition of copal, sandarac, and similar materials to produce the effects he had seen in the paintings of the Old Masters. Maybe his oil really did need them, seeing that the recipe went through a dull, wet phase. Perhaps when actually used as a glaze it doesn't look so good. One would have to try it.

So why not just add a little resin? You could, but you're introducing a point of failure (resins, compared to good oils, do not behave themselves very well, from the standpoint of conservation), and you'll have to give up on eliminating volatile solvents from your studio. Remember, too, that transparency, a product of low pigment saturation relative to medium volume, and gloss, an effect of its dried surface, have nothing to do with each other. If you want that surface to shine, paint the picture with oil, and when you've finished, put the varnish on top where it will actually do something. (Store, as you might expect by now, had retained both gloss and wetness.) Resins can alter paint handling for the better, though, depending on your idea of better. Go investigate if you're curious.

Today, Day 9, finds uniform gloss and hardness among all samples leading up to the impasto. Impasto portions of Vodka and Psyllium have skinned over, Salt's have turned gluey, and Store's remain wet.

A few days in I realized that I had arranged an apples-to-oranges comparison, but the experiment yielded useful information anyway. According to Tad Spurgeon, the Salt method dries fast and the Vodka method dries slowly. On my canvas the reverse happened. But between the unchalked oils, Psyllium dried faster than Salt, which in turn dried faster than Store. Chalked Vodka dried faster than all of them.

In conclusion:

1. Any hand-refined oil will dry faster than store-bought, even good store-bought.

2. Chalk conditioning makes a big difference to drying time. Apparently it overwhelms disparities in drying times inherent to various hand-refinement methods. (This hypothesis could use some more testing.) If you have a lot of store-bought oil around, you might try shaking it with one tablespoon of chalk per one cup of oil and letting it sit open for a while to see if it firms up faster. When I was at the studio on Saturday I shook a tablespoon of marble dust (which is just a dense form of calcium carbonate) with a cup of Gamblin, so we'll see how that turns out.

3. Salt water refinement has nothing going for it except for low expense. You have to tend it for three weeks, while Vodka takes a day, and Psyllium takes a few hours. It dries faster than store-bought, but not as much as other, easier recipes. I also chalked my Salt batch to see if it starts to compete with Vodka after conditioning.

4. I'm missing a useful comparison, that of chalked Vodka to chalked Psyllium, or unchalked to unchalked. The above results indicate that chalked and sunned Psyllium might dry really damn fast. Ethanol-refined linseed oil has the advantage of a long history, and when chalked dries as quickly as you have any right to demand of oil paint. Psyllium, a newer method, would have to fail in an unexpected way - cracking or yellowing or somesuch - in order to reject it, and I can't think of why that would happen.

4a. Okay, I can think of one reason. Acidity, considered very generally, contributes to the yellowing of art materials. If you soak psyllium in water, the solution has a pH as low as 6.62, according to a thing I found on the Internet. Since chalk can take water all the way up into the low 8s, chalk conditioning ought to neutralize any acidity added by psyllium, assuming that it exists. For that matter, vodka has a pH of 4. Probably none of this matters but I'm leaving the item here just to record that I thought about it.

4b. Spurgeon doesn't get into psyllium filtration. Its discoverer, I gather, feels proprietary about his method. I figured out my own method, however, and I don't: Stuff a cotton ball into a funnel and place it over a jar. Fill it with a half-cup of whole psyllium husks. Pour 1-1/2 cups of cold-pressed, unrefined flax oil over them and let it seep through. Refrigerate the results for four hours (or for convenience, overnight) to see if it clouds. It likely won't, but if it does, filter it through a new batch of psyllium husks. Otherwise, you can condition it by shaking it with a tablespoon of calcium carbonate, exposing it to seven days of sunshine, or both, with that order recommended. (I like to use a glass-topped casserole dish for sunning.) The recipe scales if you have the appropriate funnels and jars. Store with the lid atop the jar but don't screw it down. (Otherwise, over weeks, chalked oil will glue the lid closed, then form a formidable vacuum that may oblige you to pound a nail through the metal to get it open again.) Alternately you could take the lid off and rubber-band some cheesecloth over the top.

I already described the vodka refinement recipe but really you should buy Spurgeon's book if you want to explore. Other things count in life besides drying speed. Each of these formulations, store-bought included, have their advantages, and Spurgeon examines them. I like Spurgeon's take because he regards none of the wisdom recorded in the book as normative. From early in the text:

This book explores the relationship between the philosophical and the practical, documenting one search for greater awareness of the oil painting process in relative detail. Its materials and techniques are not presented as historical reenactments, or definitive; it is simply a record of what worked for me, and why....The reader is gently urged to consider the potential of the materials when addressed on their own terms. Overarching attention to detail is both the foundation of the universe, and the functional basis of any creative process. Once observed, these details accumulate to form natural systems whose components are logical, yet unfathomable otherwise. Creating a dialogue with the materials incrementally, from the inside out, produces far reaching results for the life, the work, and their unique partnership at the easel.

I'll keep an eye on the drawdowns but I don't expect more revelations. A proper impasto would have much more pigment in it than 2:1 color to oil by volume, like these piled-up glazes. Less oil by proportion means less stuff that has to dry. Proper paint ought to harden up pretty quickly. Time to find out, in some art.




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