I was wondering how much medium one could safely add to glaze layers.I remember the question being asked years ago on the old AMIEN forum, and there didn’t seem to be a clear-cut consensus. One reply suggested that the ratio almost didn’t matter, as long as the glaze was applied thinly enough. In the opinion of the moderators, how much leeway do we have regarding the amount of medium in very thin glazes? Let’s say we have a glaze which is half paint, half medium, brushed on then patted down with a sponge – basically tonked – leaving more or less a residual stain of colour. In a glaze layer this thin, is the high amount of medium likely to cause any problems? I’m assuming if yellowing is a problem with oiling out, it might be something to worry about here too. And could we expect several ( similarly extra-thin ) layers of glaze, applied over each other, to develop the same problems that a single, thicker layer of medium-heavy glaze might, yellowing or even wrinkling? As always, any advice would be greatly appreciated.
Thank you Brian. I usually use Gamblin’s Solvent-Free Fluid, which is 100% fat. The Gamblin technical staff are careful to advise a twenty-percent maximum, however the paint is applied. I try to keep it at around ten percent. Normally I oil-out the area of the painting to be glazed, rubbing the Gamblin medium in with a finger and dabbing off the excess, rather than adding extra medium to the paint itself; the slightly more slippery surface makes it easier to brush the paint out thinly, and ( I hope ) there is less medium involved overall. Still, it sounds like I should be cutting the Gamblin SFF with solvent when oiling out. If I could trouble you with one more question : an Australian company makes a clear oil paint which is Alumina Hydrate in sunflower oil. It seems like a good way to add transparency to glazes and titanium whites, without worrying too much about amounts and ratios, as we have to with mediums. But are there any issues with Alumina Hydrate I should be aware of, and should I be wary of overusing it?
Thanks very much Brian. Your advice is appreciated and, apparently, much needed – I would have definitely gone ahead and merrily overused the aluminum hydroxide in everything I could think of! I will start looking into these calcite/oil mediums. Thanks once again.
I am not sure that the answer is going to be any more exacting than that given on Mark Gottsegen’s AMIEN. I do need to ask first, what medium? Anything containing a soft resin should be avoided but if used should be only added in extremely small amounts to minimize paint solubility. The medium recipe would greatly influence how much should be added. A medium containing large amounts of solvent could be added in larger proportions than that containing only oil. Alkyd mediums contain solvents and come in different viscosities. Mixtures of oil and calcite are inherently leaner and could be added in slightly larger amounts. Yellowing and potential wrinkling are related to superfluous oily components. Your procedure does seem like it would minimize the physical amount of glaze on the surface. Certainly the thinner the layer the better and this would go a good way to mitigating negative effects. Minimizing oil is also very important and the crux of your question. I am not sure that you could put an exact percentage on this. There are too many factors. Really, one should use just enough medium to allow one to create the effect one is attempting while also using mechanical means to help thinly distribute the paint. You sound like you are doing this and while I do not know your medium recipe, you appear to be using a sound method. Sorry I could not add anything more precise.
Aluminum hydroxide or “alumina” has been used as a thickener and stabilizer in oil paint for very long time. It, like aluminum stearat,e creates a gel when dispersed in oil. A very small amount added to an oil paint helps to keep the oil from separating from the pigment, this has been seen as useful, especially for very heavy pigments that want to fall out of the mixture. An excess (beyond what is required to aid is stability) has always been seen as an adulterant. If you buy those really cheap 200 ml tubes of oil paint that sell for 10$ irrespective of the pigment, you are basically getting a tube of aluminum strearate or aluminum hydroxide gelled oil with enough pigment to provide color. This is why student grade paints have a much lower tinting strength than professional grade paints. Aluminum hydroxide is also the primary material in a tube of alizarin crimson or rose matter (this is the substrate that the dye is coordinated onto). Paint these paints out and you will see that their films are rather rubbery and insubstantial. The medium that you mention would is somewhat similar to those touted quite a bit lately composed of a thickened oil and calcite, although I would personally really prefer the calcite/oil mixture as it forms a firmer film with oil than does alumina. I have a tube of a similar medium made by a US company that is 20 years old or so. The residual medium around the tube opening is just as brown as that seen at the opening of an old bottle of drying oil. Additionally, none of these low refractive index fillers (aluminum salts, calcium fillers) mask the yellowing of the oil in the way that many pigments can. I would treat this medium and those like it as if they were slightly leaner painting mediums and limit the proportion so that you create a solid paint film that does not inordinately yellow.
