Hi. I'm doing more metalpoint ground experiments and have a few questions.
1. Does anyone know relative hardness (i.e. which is softest, which is hardest) of a cured film of the following binders: gum Arabic, egg yolk, casein, acrylic polymer, vinyl polymer, and oil? I'm primarily working with water-based metalpoint grounds, but I made an oil ground and found that it works really well; it seems to abrade better than other surfaces, once it has fully cured. So I'm wondering if an oil base is that much harder and resistant to a metal nib than the above water-based binders.
2. Gordon Hanley is a metalpoint artist who, apparently, (as seen in online reproductions of his work) achieves authentic blacks in his drawings (whereas most metalpoint artists get no more than deep grey). He says he gets black by working with pure silver on a homemade, proprietary ground. Many metalpoint artists would like to know his secret, but he stays mum.
I made an oil based ground that consisted of 1 part Gamblin Brilliant White Oil Paint, 1 part silica, 1 part Liquin. Not sure how durable such a combo is, but it did yield very dark marks - and, after sitting for a few months, I just noticed that one set of marks now appear genuinely black. (To my annoyance, I didn't note what metal nib made those mark). The questions are: how durable is that combination of ingredients? And is there anything noteworthy in those ingredients that might account for deep grey metal marks turning black?
3. I've played with adding different extenders (silica, bone ash, glass, barite, pumice, marble dust, chalk, historic pigments) to metalpoint grounds, to increase abrasion. Silica gives the best results, which isn't surprising given its Moh's Hardness Scale rating of 7 (harder than any metal nib I use). What is surprising is that Talc, with a MHS number of 1 (much softer than my metal nibs) also seems to minimally increase abrasion. I've read up on the properties of talc but it's confusing for a non chemist to distinguish between natural versus milled state, etc. - I just don't understand it all. So my question is, does anyone know properties of talc (i.e. does it have an unusually rough morphology?) that might explain why it improves a metalpoint surface? Is it accurate that all minerals, even after they've been milled, have an irregular morphology (versus, for example, some modern pigments that are quite smooth and round at the particle level)?
Thanks as always, Koo Schadler
