MITRA Forum Question Details

Hi

There are a couple of separate issues here. First, there is no evidence to suggest that oil of spike is less toxic than Gamsol, which is a very pure odorless mineral spirits (meaning that aromatics and other more toxic fractions have been removed). These highly refined aliphatic solvents are probably the least toxic organic solvents that are miscible with oil paint. It is important to realize that there is a very different “feel” under the brush between “regular” mineral spirits, OMS, gum turpentine, oil of spike, etc. This may be mitigated, obliterated, or augmented depending on what other components are added to the diluent.

Spike oil is probably most useful due to its very slow evaporation rate, this can be exploited for certain technical effects. It is not without its dangers, though. It’s very slow evaporation rate also means that using this solvent in subsequent and upper paint layers can allow for the biting into and disruption of lower layers. Unlike paints like gouache, which can be rewet many times, biting into and dissolving semi-dried oil paints irreversibly diminishes film strength. This is not to say that one cannot use oil of Spike responsibly, but I would restrict its use to ala prima or to paintings with relatively few and well-dried layers.

As to over use of diluents contributing to a weakened oil film, think of it like this, while in theory a diluent is not changing the percentage relationship between pigment and binder, there is a point where pigment particles are so separated and the binder so attenuated that the resulting paint film is friable and underbound. This situation is not uniform for all media. It is important to realize that drying oils are not really great adhesives and their ability to bind pigments is rather limited. Acrylic dispersion binders, on the other hand, can be thinned to a great degree and still adequately bind the paint film (within reason).

As to walnut oil, it produces a slightly less resilient film than linseed oil. Linseed oil certainly creates the strongest paint film, but walnut oil may skin less readily, resulting in less wrinkling of thick paint films. This is not universally agreed on and some blame the paint defects in early 16th century Italian oil paintings on their use of walnut oil. We at MITRA feel that, until there is conclusive evidence, walnut oil it is a perfectly reasonable binder for oil paint.

As far as “less yellowing” much of the current thinking about this phenomena is that the three major (highest grade and selected for color stability) drying oils do yellow at different rates, linseed the soonest and poppy the last, but that, over time, they all yellow to somewhat the same degree. With this in mind, we feel that it is probably more important to choose drying oils based on their handling and film forming qualities.

I hope that was of some help.

​Stand oil is different...it tends to yellow less, takes longer to dry, and creates a more flexible film. The problem is some highly viscuous stand oil mediums are not easily thinned using Gamsol as a solvent...You might find our document entitled "Mediums and Additives" in the Resources section of interest as we go into some detail on the various types of oils used in painting.

Brian, interesting point about the assumption that Oil of Spike Lavender is necessarily less toxic than OMS. Where lavender essential oil is concerned there simply isn't anything like the record of heavy, long-term exposure to spike like there is with turpentine. We know a lot about risks associated with turpentine largely because of its extensive history in the ceramics industry, where there was widespread, heavy exposure over many years, and a detailed record of the consequences.