MITRA Forum Question Details

​Walnut oil has lower viscosity at room temperature than many other vegetable oils, so that may lend it greater lubricity. Viscosity describes how a fluid deforms in reaction to force, and low-viscosity fluids like walnut oil don't take much to get them squidging around. Slipperiness in oil is largely related to the non-polarity, shape and organization of molecules and the degree (or lack) of bonding between these organized structures. Oil molecules are really good at sliding past one another without sticking, and that makes oil feel slippery.

​I'm not a paint chemist, so I will pass on giving anything that might be taken as an authoritative answer. Just anecdotally, I have not noticed increased slippery feel to oils that have gone rancid, which (if I understand correctly) should contain more free glycerol than fresh or refined oil. (Best guess, anyway.) I was not able to find a comparison of vegetable oil viscosities that included poppy.

​Typically, vegeyable oils do not contain glyercin in a free state, unless the oil has undergone hydrolysis. Any vegetable oil is "slippery"—it is simply the nature of an oily substance. However, as the molecular weight of the oil increases it provides more resistance and feels less slippery. Walnut oil has a lower kinematic viscosity than linseed oil that may lead one to feel that is more slippery.

Thanks so much Matthew and George. I have been at a Rembrandt conference in Amsterdam and have had little chance to check here. You guys are so great to cover these topics so well.

A beeswax In solvent or bees wax in a solvent/oil/resin medium will contribute great lubricity. It also contributes permanent solvent sensitivity if it is used in more than a very small proportion. If you do this it will probably be best to not varnish your work and you should record your paint and medium ingredients and relative proportions somewhere on your painting (see the resources section for suggestions about how/where to do this). The downside to this is that wax does attract dust if used in larger proportions. However, an oil/wax medium is certainly viable method.