Hi, I’d really appreciate some advice on an unusual query; I’ve been referred to this amazing website through the Painting Best Practices Group on Facebook. I’ve had a good look through the resources and forum threads on here, but I still have some questions:
I’ve been asked by a jewellery designer if I could paint miniatures in oil paint onto slightly concave 22ct gold ovals, circa 1mm thick, to be set into a bracelet. I’m wondering what a concave surface will do to the paint layers over time.
I’ve previously painted on convex gold domes for the same client, treating it like painting on copper/on top of gold leaf (there was limited testing I could do on solid 22ct gold!): the gold was completely obscured, as it was purely to make sure the whole jewellery piece was made of precious materials. I very lightly abraded the gold, degreased it with denatured alcohol, then two thin coats of a flexible primer: Liquitex clear gesso primer (chosen because it was difficult to scrape off copper that had been prepared in the same way. It was also quite difficult to remove from the gold dome two months down the line, i.e didn’t peel, when I removed the finished painting to make way for a new design). I then painted in very thin layers using the minimum amount of medium: progressively fatter turps and linseed oil. The final paint thickness is very thin. 6 months on, the convex domes appear unchanged (if 6 months is a reasonable cure time? I’m expecting the cure time to be slow because of the circa 1mm thick metal support, but it is very thinly painted).
For the concave domes, I’d be using the same process and medium.
– Is a concave surface inherently unsafe for indirect oil painting?
– If not, would an alkyd primer, or a lead-based primer be a better product than the acrylic gesso primer? I’m working on the assumption that the gold is largely chemically inert, with circa 2% copper and circa 6% silver – I gather lead primers bind chemically to copper, but my only option (as I’m in the UK and lead products have been phased out) is an old tube of Daler Georgian Flake White – it doesn’t say if it contains zinc, or if it’s linseed oil. I don’t know if this would be up to snuff as a priming layer at all.
Thank you for reading this long-winded post!
Thank you so much for your thorough and speedy answer, Brian! It’s lovely to have your sound advice – it’s been a very long research process trying to muddle my way through! I will research the cues you gave me.
Re. the choice of a flexible priming layer (the acrylic dispersion), it was just me being worried that the priming layer might contract and be stretched over the dome as it cured, so I was worried about cracking down the line. There isn’t much stress to the painting in fitting it into the jewellery as the support is thick enough to be rigid, and it’s not a push fit/solder but a screw fit.
Re. varnishing, the support is solid 22kt gold, circa 1mm thick, so there’s no mordant to worry about happily! The only reason the support is solid gold and not an insert is to keep the whole jewellery piece made of precious materials – it’s completely obscured by the painting, although the gold is visible from the back of the piece.
Yes, all the pieces are/will be varnished – it’s a tad convoluted however: the first set of paintings, without glass, were varnished with Gamvar when hard dry (I used a dental tool instead of a thumb given the scale!) as speed was important. Then the pandemic hit and the launch was set back anyway – so I now have the opportunity to put a more durable varnish on those pieces, given that they are 6 months cured, removing the Gamvar first. My current thinking after researching it best I can is that a high molecular weight polymeric varnish like Golden MSA or Conservar Polymeric Varnish would provide a more durable, and thicker, layer – I may then have to add a layer of Gamvar on top to try and restore its previous appearance…
The client is considering putting Sapphire glass over future pieces as a protective measure; in this case, I would still varnish them to saturate the appearance, using Gamvar as it’s not exposed to wear and tear and is purely an aesthetic decision.
Whether the sapphire glass would cause problems is another research question for me – I’d really appreciate your advice if you have time! Currently, I’ve got as far as this: it would be safe to add glass over the painting, spaced away from it, once hard dry and post Gamvar, as the oxygen in the paint film is sufficient to keep the curing process going, bouncing in and out of the paint film and being recycled. The dome wouldn’t be soldered in place, only a tight screw fit, so as far as creating a microclimate between the glass and the gold is concerned, I don’t know if there’d be any issues with trapping moisture – as there wouldn’t be any water in the paint film or support, and presumably as there’s no air gap no moisture can get in? I can’t find any examples of a sealed, non-porous support, non-aqueous medium painting – although I’m sure miniature portraits on copper have been placed in lockets behind glass.
Apologies for another long and rambling query! Thanks again for your time.
Ellie
Thank you, Brian! That’s great to hear. (no worries, I assumed I’d just been cheeky in expecting answers to such long and convoluted questions!)
Best wishes, Ellie
I really do not think that concavity of convexity of the rigid substrate would add any additional complications other than it is harder to paint on such a surface.
It seems to me that your procedure is sound. I see no benefit of using an oil ground on a metal surface in this instance, since this is really just a first application of oil paint, not really different than subsequent applications of oil paint. If you needed an opaque ground layer because your later oil paint layers would be transparent, that is a different situation. If your acrylic dispersion layer adheres well, it is likely a fine system. However, there are resins that are more sympathetic for most metals. The acrylic B48N resin is often used in conservation to coat metals as it has particular affinities for metals. Since the metal in this case is inert, this may be unnecessary. It is insoluble in mineral spirits so it could be used if that is your oil paint diluent. As to alkyd primers, you would really need to do a test to see if they are superior. They would provide the benefit of being insoluble in most organic solvents after oxidization.
This brings me to the subject of varnishes. Are these varnished? Is it possible that the varnished would need to be removed at some point? If the answer is no to both questions then the answer is easier, just pick what works best. If the answer is yes, one needs to be thoughtful of the solubility of the gold mordant (is the gold adhered with a dispersion or oil mordant, and what are the solubility issues) and the solubility of the initial “size” or “ground” layer.
You mention flexibility of the “size” or “ground” layer. Why is that quality needed here? Is the substrate likely to be stressed or deformed when insetting into the bracelet? Perhaps that could be an issue and if so, you would ant to adhere them before the paint becomes overly brittle. Likely this in not a problem.
You are correct in stating that the scuffed predominantly gold surface is unlikely to tarnish or corrode and should be quite stable in terms of chemical reactivity.
6 months seems like a reasonable cure time. Personally, if you are painting the oil paint thinly and in very few layersand on a relatively slick surface, you want to make sure of adhesion in this situation and not worry as much about issues relating to complex layering. If it were me, I would probably progressively add small and judicious amounts of a quality alkyd medium to provide a bit more adhesion.
I see that I did not return to answer your additional question. I would think that the glass would be fine as long as the paint has dried long enough to be varnished. You would not want the varnish (or paint) to touch the glass but it does not appear that this would occur in the scenario you laid out.
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