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Wednesday, January 24, 2018

Water-miscible oils

They’re marketed as easier and safer than traditional oils. Are they?

Fitz Hugh Lane Day at Camden, by Carol L. Douglas. This would have been impossible to paint with water-miscible oils. They run at the first hint of atmospheric moisture.
Yesterday I got a note from a fellow professional mentioning that she’s finally seen the last of her water-miscible oil (WMO) paints. I was surprised she’d lasted this long.

Water miscible oil paint is engineered to be thinned and cleaned with water, thereby avoiding the supposedly-harmful use of turpentine. But few painters use turpentine anymore. It has been overwhelmingly replaced by odorless mineral spirits. Still, WMO are perceived as somehow ‘safer’ than regular oil paint.

Of course, the toxicity of paint rests not in its binders, but in its pigments. The heavy, or toxic, metals like copper, cobalt, cadmium, and lead are the worst. It’s impossible to avoid them completely, but when you buy paints, consider not just your own safety, but that of the poor schmoe in China who has to make them.

Traditionally, pigments were made in a binder of drying oil—flax, walnut, safflower or egg yolk—or gum Arabic, in the case of watercolor. All of these binders are organic, by the way. In the 20th century, we saw new binders developed, including alkyds, vinyl and acrylics. Water-miscible oils are in this class of engineered polymers.

Squall on Lake Huron, by Carol L. Douglas. I got soaked; so did my painting.
Most brands add an emulsifier, or detergent, that allows the linseed oil to accept up to 25% water by volume. Since emulsified paint rapidly becomes stodge, it’s wise to use as little water as you can with these paints.

Holbein’s Aqua Duo manipulates the polymer to accept water in a loose bond at the end of the chain. These paints contain no detergent. They tend to be less gummy than other WMO. However, they are marketed to be mixed with acrylics. Acrylics and oils dry so differently that this promises to be an archival disaster.

When this happens, the oil painter ducks, but can save his painting. WMO are immediately ruined.
WMO are designed to handle like oil paints, but in practice, they don’t. When thinned to a wash using water, they may refuse to adhere to the ground. At middle thicknesses, they dry more like gouache than like oil, with a flat surface and color shift. As impasto, they have the consistency of oatmeal. Like acrylics, their transparency changes as they dry. The paints have a different flow rate than conventional oils, so you can’t really place a long, lovely line with a loaded brush.
              
All oil paints dry through oxidation, but first the water-soluble oil must disperse the water through evaporation. That leaves the final surface slightly tacky to the touch.

Oil painters have been known to pick off the water droplets right before a sale. That's impossible with WMO.
Most paint looks pretty good the moment it’s applied to a canvas. The question is, what will it look like when it’s been drying for a few hundred years? Oil paints develop cross-linked polymers that create a strong, tough surface over time. How will the emulsifier in water-miscible oils affect that? I don’t know, and neither does anyone else. They haven’t been around long enough.

How do manufacturers suggest you work around the technical limitations of WMO? By adding oil-based media to their product line: stand oils, quick dry media, or alkyds.

All of which defeats the purpose. Here’s a news flash: traditional oil painters wash our brushes with soap and water, too. I use a saddle soap, but any super-fatted soap will do. That’s because soap—like detergent—is an emulsifier. Soap is made up of molecules with different ends. One end loves water. The other end loves oil. It’s the same principle as the detergent in water-miscible oils, but applied at the end, where it can’t harm your painting or technique. Just rinse the solids out of your brush in your slops tank first, and you'll find that oil brushes wash easily.

2 comments:

Corinne said...

Very helpful and thought provoking article. I may need to go with true oil paints and give up the WMO saga sometime after I use up all I've invested in WMO's. Thanks for all the research you've done to educate me....

Michael Chesley Johnson said...

I tried water-miscible oil several years ago from two different companies. I didn't like them. It's good to know I don't need to change my opinion. :)