Oil Paint on Convex and Concave Solid 22kt GoldApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2021-05-01 10:14:21 ...
Most recent comment 2021-05-15 05:20:45
Rigid Supports
Gilding
Oil Paint
Grounds / Priming
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!
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Moderator Answer
(brian baade)
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.
EditDelete
Moderator Answer
(brian baade)
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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