Gold leaf has been used to decorate all sorts of different things. I think all the visual arts must have used gilding in some way or another at times. There are many different ways of sticking a thin layer of metal to something. You can glue it on, melt it on or chemically adhere it to a surface. In my work I am only using adhesion with a glue or other mordant.
Gilding on furniture
Antique furniture and picture frames are water gilded onto a clay base (bole). First, the timber work is finished and then sized with glue. Then it gets several layers of Gesso which is made with chalk or whiting (calcium carbonate) bound with rabbit skin glue. This is then coated with several layers of bole (fine clay in glue, usually red). The bole is burnished to a silky smooth finish. It is then wetted with water size and the leaf applied. It can be burnished with an agate burnisher to a very highly reflective lustre. It is sometimes gilded with plain water and some practioners use a drop of methyl alcohol to increase its wettability. The rabbit skin glue in the bole does the same job as the gelatine in water size for glass gilding.
By similar means gold leaf will stick to gesso (genuine, not acrylic) and is used in illuminated manuscripts in essentially the same way. After the design is painted with gesso it is scraped to smooth it down. You simply breathe on it to moisten the gesso then apply the leaf.
Oil gilding is used in all exterior applications for sign work including vehicles and carved timber signs. The lettering is simply painted with a suitable oil size or gilded during it's whistling tack. Whistling tack is the time when the size is nearly dry. It can be touched lightly without it damaging and wont stick to the finger but has just enough tack left to take the leaf. If you drag your finger on it there is a kind of whistle noise. Names on honour boards are also oil gilded. By tradition, some yellow paint is added to the oil size so that you can see it on the timber background.
Gold is oil gilded on many materials including stone, marble and granite for graves and stone monuments. After the carving is done, the area to be gilded is sealed and coated with an oil size. This gradually dries and develops a surface tack whick the gold is stuck to. Similarly, decorative plaster is sometimes embellished in the luxurious interiors of yesteryear. The highlights are oil gilded to enhance the light reflections. Especially effective on foliage and scroll decorations.
Leather is sometimes decorated with gold using a method called gold tooling. When leather is used on desks and table tops , it often has a fancy gold border. A resin powder (mastic gum) is spread on the leather and the gold leaf in ribbon form (on paper) is laid down. A hot roller with the decorative pattern in relief is pressed onto the ribbon. This both embosses the leather and melts the resin making the gold adhere.
Ceramics and hot glass
In ceramics, gold is dissolved in solution and applied as a brown liquid (lustre) and when fired, comes out bright and shiny. There are several coloured lustres and many different methods of achieving a metallic finish.
In glass blowing, gold leaf immediately sticks when touched by the molten glass. It breaks up in a series of very fine cracks when blown.
In an old technique used to gild building domes, gold was mixed with mercury (quicksilver) to make an buttery amalgam. This was spread on building domes and heated to release mercury vapour. I believe it took a couple of coats and heatings to bring up the lustre as well as scrubbing with vinegar.
Don't try this at home kids. I suppose a few thousand artisans dying of mercury poisoning was a small price to pay for the glory of some autocrat. Incidentally, mercury was also used in gold-mining to leach the gold from the ore.
This is a chemical method closely related to silvering. A reducing reaction is used to deposit metal onto a surface. It is often used on glass turning it into a mirror.
Gold dissolves in cyanuric acid and can be deposited in an electroplating bath. This is a whole separate industry of course with many proprietry chemical blends and varying methods. Brass will take a gold plate well. Cast metals, if excessively porous, may be given a copper plate first as a filler, buffed and then gold plated.