As with the above image, this image is one that I have painted several times. It is a copy of a Sassoferrato. Although it is not exact, I like to paint this image when testing a new medium, as it permits me to see how each behaves in a full range of values, and in glazes.
In the past, I used the word amber to refer to both Baltic amber, and to hard copal resins. Although, upon just looking at the raw resin, they can appears simliar, they really are different materials, and create much different effects, when used in paint.
This is an oil painting 11x14 inches. In the underpainting, I used a medium containing oil of spike, and Canada balsam. I wanted a very smooth surface for the later paint layers, and this medium worked wonderfully. For later layers, I used copal, employing slightly greater amounts of linseed oil, with each sucessive layer. I also added a color called Stil de grain, to the varnish, in very small amount, to create a slight patina. Rather than purchase this color (stil de grain) as a separate color, it can easily be mixed by combining something such as Winsor and Newton's Indian yellow, with a touch of raw umber. That way the colors are much more versatile, and can be used for other purposes as well. The copal worked wonderfully, and in the end, although the picture doesn't convey it, it created an enamel like hard glassy surface similar to those I have seen by Flemish masters, in quite a few museums. This is much different than the surfaces produced by alkyd mediums. In the end, I applied a very thin layer of amber varnish, over the entire surface. Several drops, which were subsequently spread out super thin, over the entire surface.