Renaissance Materials made by Dr. David Cranswick. Liquid Glass Mediums.
Liquid Glass 16th C. Glazing Medium
The recipe for this glazing medium dates back to the early 16th century, it imbues a quality of rich translucency in the shadows and a jewel like luminosity to the lighter colours. Unlike modern glazing mediums the glaze medium of the ‘Old Masters’ was a much thicker vehicle and did not contain any turpentine or solvents. This medium facilitates the building up of the painting in layers of transparent glaze; by this method the light is literally “trapped” within the paint layers, giving to the painting a sense of ‘inner light’ and luminosity, at the same time the darker tones are made translucent, imbuing depth and atmosphere into the shadows. Due to the high resin content of this medium one can blend one tone or colour into another with great ease, while at the same time the colours retain their character without becoming over mixed and muddy.
As with most substances of quality, it is only through the correct method of application that the real virtues of such a medium are fully exhibited.
For best results the medium should be thinned with approximately 15-25% walnut or poppy oil (do not thin with turpentine). In accordance with old master practices, the medium should be applied thinly with a hog hair brush over the entire surface of the painting, sometimes adding a warm transparent earth colour such as burnt umber into the glaze to give an overall warming tint. This glaze should then be repeatedly rubbed back for several minutes using the edge of ones hand until only a very fine film of glaze remains, (if the glaze feels greasy or oily under the hand then one needs to rub back more). The surface, when ready should have a satin finish and should not be obviously glossy. One then applies the paint into this wet glaze, building it more heavily in the lights whilst keeping it thin and transparent in the shadows.
One should not attempt to thin the paint with more glaze, the wet glaze into which one is painting is sufficient to give all the variety of character to the paint that one needs, thinning the paint with more glaze will only make the paint unnecessarily oily and difficult to control. If it is intended to continue painting the the next day one should add a few drops of cobalt siccative into the glaze before applying, as such this glaze remains wet and workable for five or six hours. [Quantity example - 3-4 drops for covering a 2ft by 2ft canvas]. One should begin each painting session with a glaze of this medium into which one then further develops the colours. Always make sure the painting is fully dry before applying a glaze upon it. In certain cases, where one wishes to add more ‘flow’ to the paint one may add a little glaze into the appropriate colour. But the usual practice is to first apply the glaze over the (dry) painting and then to paint into this glaze having first rubbed back in the methods described above.
