Week Six: Cleaning Gilded Areas

Hi, today I would like to talk to you about the gilded areas of the Bishop Saint with Donor.
	This painting has many areas that have been covered with real gold leaf, such as the robe of the Bishop and the background. Many of these areas have a small relieve to give a better sense of three-dimensional reality, such as the Bishop’s rings and the brocades on his cloth.
The gilding was done before any paint was applied. First, the reliefs are made by modeling a thick paste made with animal glue and a filler. Then a layer of "red bole", which is an earth pigment mixed with animal glue, is applied only on the areas that are going to have gold. The color of this under-layer gives a warm tone to the gold. Next, a coat of water is applied on the red boled areas and soon after, the gold leaf is laid down. The water makes the glue present within the red bole layer slightly sticky, and this is enough for the thin gold leaf to be attached. This method of gilding is called "water-gilding".
	After all the surface is flat and gilded, different designs can be indented by using punching tools. When the painting was hanging in its church, the indentations on the gold, would have provided small surfaces for the candle light to be scattered in different directions, producing an almost magical twinkling effect of the surface.
	Originally, gilded areas would appear to be like solid carved gold. But since gold leaf is very thin, it can be very easily abraded and now the red bole layer can be seen throughout the surface.
Gold leaf is also very sensitive to both water and organic solvents. Therefore, the varnish layer could not be removed in these areas. In the future, better techniques might be able to remove the varnish layer safely, just the same way that we now have better techniques than they had in the past. Moreover, the discoloration of the varnish on the gold is not particularly distorting the image.
And that’s all for today. See you next week!

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