After the gesso has dried it can be sanded smooth, for this I use aluminium oxide paper in 280, 400, and 800 grit. If very little sanding is needed then the gesso can be smoothed with damp cloths. Usually on a frame that is being gilded and painted, the areas not being gilded are only given a quick rub over, as the texture from the brushing or spraying of the gesso can add to the paint effect. I would also only usually apply bole to the areas being gilded.
Bole is very fine clay that is mixed with rabbit skin glue. The most often used colour is red, although it comes in various other colours, that can be mixed to get various shades. The colour of the bole will have a subtle effect on the perceived colour and warmth of the gold leaf, also some boles will burnish better than others.
Sometimes the bole can be burnished before the leaf is laid, this can be done with a stiff brush, a cloth, or an agate burnisher and has an effect on the appearance of finished gilding.
Bole can be bought in dry or wet form, I use wet bole which is mixed with rabbit skin glue (varies from 1:13 to 1:15 strength glue/water), the approximate bole to glue size mix is 1 part bole to 2 or 3 parts glue size, although this is really only a rough guide. The bole is added to the size a little at a time, using a clean spoon or knife each time you take more bole, to ensure no size gets into the bole storage container.
Once the desired consistency is reached the mixture can be strained or filtered to get rid of any lumps. The bole is brushed on the frame, and the number of coats usually varies from 4 to 6. Each coat is applied when the previous coat has dried matt or enough so there are no glossy/wet areas, but as with the gesso, the surface should not be allowed to dry fully before the next coat is applied.
