Something new: Amalfi blue bole. For the uninitiated, clay bole is the undercoat used in traditional water gilding. Water gilding allows the gold leaf to be burnished to a brilliant lustre and as a method that has been traced back to at least 3,000 BC, little has changed in its' preparation. A protein binder (size, such as rabbit skin glue) is applied to wood to seal the surface and provide for proper adhesion of gesso. The binder is then mixed with water and a filler, usually calcium carbonate, to make the gesso. When dry, the gesso is sanded or water-polished. After this the bole and size mixture is applied.
As gold leaf is somewhat translucent, the color of the bole will affect the look of the leaf, especially if and when the leaf is abraded, either intentionally or through natural wear over time. Amalfi blue is fairly light with an almost aqua tone. It looks quite nice with a 22 or 23k leaf as well as 12k white gold.
One problem with blue bole in the past was its interaction with genuine silver leaf or with the silver present in white gold, eventually discoloring the leaf। However, the manufacturing process for blue bole was changed in the last few years to eliminate the tarnishing effect. I do find that it's important to polish the bole well before gilding as it can dry somewhat stiff and gritty. Polishing then allows for a very smooth and attractive burnish.