Hi David,

Gold leaf actually has interesting optical properties at the quantum
level, but it is also somewhat transparent, and not fully opaque. So
gilders use different could bole - yes, bole - paint under the leaf to
achieve different end colours, for example yellow, reds, and greys are
often used. Yellow will make a very brilliant 'gold' gold.

Also, the different shades of gold are available due to the fact that
you can get gold leaf in anywhere from 12 to 24 karat varieties, and
this affects the colour. Also, metals such as silver or copper are
added to the base gold to achieve different colours. You can can get
very nice greenish gold, all the way up to very strong yellow.

Painting the underlayer vermilion can be done to allow irregularities
to show, but is normally to modify the effective leaf colour. I like
to use yellow underneath for brilliance. Medieval painters often used
a dark plum ground under gold to achieve a noble and sombre effect.

As a final point, I must mention that gold can be beaten so fine that
is is truly optically transparent. It was possible to buy Kodak
Wratten filters for photography in the 1950's-60's which were green to
yellow and made from gold leaf beaten to a specific thickness (the
quantum properties I referred to above) and sandwiched between glass.

Andrew



On 16 February 2016 at 12:11, Kelzenberg, David C
<[log in to unmask]> wrote:

>
>>>>For example you can buy what is called green gold leaf, or lemon gold leaf, and so on. So gilding can have a wide range of effective shades.
>
> I've not seen this, but I assume there is some alloyed metal used as a coloring agent?  Of course, pure gold is always the same color.  I would think the gold would have to be *very* thin to allow an underlying color to "bleed through" (in fact I would not have even thought it possible--it seems very opaque).  I remember when my instrument was being decorated, Pete insisted on painting the moldings before gilding them.  He knew there would be little imperfections in the gilding of the highly irregular surface, and wanted Vermillion to "peek through" in those spots.

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