The gold, thanks to its luxuriousness and sheen that is able to give to any objects, has always been the most widely used metal for decoration, and so there are many ways to use it.
How do you distinguish the gildings
How you can distinguish a genuine gold plating from a false one;a gilding mission by a gouache? Obviously you need a lot of attention and experience, but we can say that:
- The gilding made with real gold leaf is different from that one made with imitation gold, because gold keeps it shining for centuries, imitation gold, even if covered with protective varnish, darkens really soon. Moreover, the real gold leaf is much thinner than the imitation one, it is almost "transparent" and sometimes you can recognize the color of the underlying bolo, vice versa the imitation gold is more opaque and more flashy.
- There are no methods to distinguish the gilding mission and gold leaf, because are similar in the effect. But the gilding is always burnished, unlike the mission, and so this could be a sign of distinction between the two methods. Or using a cotton ball wet in warm water it will dissolve the glue of the gold leaf, instead he mission being often oil-based, is not sensitive to water. In general, however, the highly sculpted baroque furniture were decorated with gilding mission.
- In antique porcelain the fire gilding is clearly different from the mission, because the fire gilding is a lot more vivid and shiny.
Gold leaf (also called gouache)
This is the most difficult process, but it provides the best results. The same procedure is adopted also for the imitiation gold leaf, silver or aluminum. The following procedure is the same as the old one, with the only difference that now the gold is no more hand-hammered into thin layers, but it is industrially made.
- On a rough and perfectly cleaned wooden support, put an adhesive layer made of hot rabbit skin glue mixed with gilder’s gypsum(Bologna gypsum), but avoid the boiling, or it will lose its adhesiveness. When the plaster is ready, apply it with a brush where you want to gild. When dried you have to perfectly smooth the surface, to avoid lumps that will be clearly visible after that the gold leaf will be applied.
- Now apply the bolus (yolk mixed with red clay), that on the market is available in red, yellow and black colours. The bolus creates a sort of film, that, once dried, become the support to apply the gold leaf.
- To paste the gold leaf you have to paint a small area with isinglass diluted in water. Using the gilder's knife, lift the gold leaf and lay it on a deerskin pillow; cut the leaf into regular strips a bit larger than the area to cover. To lift the gold leaf you need a brush made with vaio bristles (an animal similar to the squirrel), rub this on your face to electrify it, then lift the strips and place them on the surface, avoiding wrinkles.
- When the glue is dried, polish the surface with agate stone (browning). Grease the agate with wax for a better sliding. Remember that the pressure may damage the gold leaf.
- For an antiquing effect, brush the surface with a mixture of water, rabbit glue and brown clay.
Due to the light transparency of the gold leaf, the color of the underlying bolus changes the tinge. In fact, to recognize the origin of a furniture, it is also useful to observe if the tinge of the surface is more yellowish or reddish. Generally if it is reddish probably comes from Italy or northern Europe, if yellowish comes from France or England.
All that is gilded in the Royal Palace has been prepared with the hand-wrought gold, whether it be furniture, picture frames or ceilings.
Gold dust gilding
The procedure is the same of the gold leaf, but instead of the foil type is requires the gold dust dissolved in gum arabic. It is painted with a brush and then polished with agate stone.
Cover the part to be gilded with an adhesive (the mission) and after drop the gold dust, that will adhere only where desired.
Gilding in rilief
Prepare a mixture of chalk, glue and gold dust to be used in very thick layers.
Gilding with mission
Cover the surface to be gilded with a special adhesive paint (called mission). When it is almost dry, but still sticky, leans over the leaf, and stick it via pressing it with a cotton ball or with an extremely clean brush. When finished, if you want to get an antiquing effect apply the same procedure used for the gold leaf gilding. The gilding mission in regard to the gold leaf can't be burnished with agate stone, and so it is less shiny, but because it is much easyer to apply, it is very useful especially for extremely sculpted baroque furnitures.
Method created in the Sevres porcelain factory in 1750. It consists of a mixture of honey with gold dust, and was used to gild small objects and porcelain. It is fixed via a low-temperature cooking. The finish is always opaque, but the higher is the temperature, more opaque it will become.
Fire gilding (mercury or ormolu gilding)
The birth of the fire gilding focus is controversial: maybe born in the fourth century b.c in Greece, but became common only in the Roman Empire; around the II-III century a.d in appeared in China during the IV-III century b.c.
It is used almost exclusively for the gold plating of the metals, but sometimes also for porcelain, especially during the Empire style period (1800-1840).
- melt gold in hot mercury;
- wet the object with nitric acid, and cover it with the mixture of gold and mercury;
- heat the object in the oven at high temperature, or with a blowtorch, so that evaporating the mercury the gold will be shown.
This process is very harmful to health due to toxic fumes of mercury and is now almost obsolete; was rather popular in the eighteenth century to gild bronzes that decorated the furniture Louis XV (Rococo), Louis XVI(Neoclassical) and Empire(later Neoclassical), but due to the premature death of many gilders, it began to be replaced since 1860 with the new galvanic gilding.
Gilding with transfer printing
Industrial method created around the middle of 1700, and used mainly for the porcelain. The color is placed on a matrix and then engraved on a suitable sheet. This sheet then is pressed on, for example, a plate, and the drawing is transferred. It is used both with the colors or gold. It easy to be recognized, because are clearly noticeable the joint of the two sides of the sheet. At the end of 1800 it evolved in lithographic printing. It has no artistic value.
Galvanic gilding (or electroplating)
The electroplating is a method used almost exclusively to give a better appearance to metal, covering it with a more noble metals such as, for example, gold, silver, platinum, rhodium, nickel, chromium, or to coat the inside of silver tableware objects. It is an electrochemical process in which, by inserting in a liquid (plating bath) both the metal to be plated that the noble metal (so used as negative and positive poles), and with electricity, the metal that serves as a positive pole lose its particles that are deposited onto the other metal. Being an industrial process it has no artistic value, and if the gilding of an ancient object is restored using this procedure, it loses much of its value.
The galvanic gilding was invented in Italy in 1802 by Luigi Valentino Brugnatelli at the University of Pavia, using the galvanic cell just invented by Alessandro Volta.