Post 471 by Gautam Shah
Gilding is a craft of applying Gold or a substance stimulating it on many different types of surfaces. Gold is applied in many different forms: gold-leaf (in sheets of very fine thickness), powder (as a pigment and as a fusible medium), as liquid or amalgam (with mercury). The term gilding also includes application of silver, palladium, aluminum, and copper alloys. Gilding is also used synonymously for plating. Modern plating can be thinner than gilding. Gilding is also used for gold laying on a surface, such as damascening, inlaying gold into a dark oxidized background, similar to niello work.
Gold leaf work is very ancient, perhaps 5000 years or more old. Gold leaf was used for tomb wall paintings in Egypt. It was also used to decorate funerary articles. Paintings, of 2250BC of VI dynasty, show gold-beaters beating the gold into foil. These types of gold leaf were more than 10 times thicker, compared to the modern ones which are thinner than paper (0.0001-0.0002 mm to 0.000001 mm). Gold leafs are produced by beating small pieces of gold placed in pages of leather or special paper leaves. The gold is pure, so does not oxidize or tarnishes. Very thin gold leaf makes it easier to cover very fine details and texture variations.
There are many techniques of gilding. Very thin gold leaf can be laid on a surface and pressed with a fine brush or swab of cotton and rubbed. The nominal texture of the surface, such as polished marble, glazed pottery, copper, steel, ivory or wood holds the leaf well. For masonry walls, gypsum plaster, canvas and such absorbent surfaces, are first covered with gesso (made of finely ground gypsum or chalk mixed with glue), and than gold leaf is adhered with an oil-based adhesive or a water-soluble size. The gilded surface is than burnished to a mirror finish. Metal, ceramic and sometimes wood surfaces are heated (metallic surfaces at a temperature less than red-hot) and gold foil applied. These are than burnished (rubbed with a hard tool or polished stone face).
For lasting finish Gold+Mercury amalgam is used. It is called fire-gilding or mercury-gilding. Armour, arms, shields, metal sculpture, furniture hardware and screens are gilded by this method. Fire-gilding was employed by China in 4th C BC for wood, pottery and textiles. Greeks used the same method for marble sculptures. Metal structures were amalgam gilded, and heated to vaporize the mercury. Romans refined the Greek gilding technique, and also used glue-based gilding for mural work. By 4th or 5th C. gilding was practised in all parts of the world.
Gilding began to be used for decorating books, scriptures, scrolls, illuminated manuscripts, made of parchment, vellum, fabrics, paper, wood and palm-leaf. These items needed soft or flexible fixing, so the gum or sizes were mixed with plasticizing additives like honey. For very fine work like writing (calligraphy) and thin line renderings of miniature images, Gold leaf application was not suitable. So transparent (liquid gums) inks with fine dust of gold as pigment was used in two manners. In the first method transparent inks were used for rendering fine work, immediately dusted with gold powder, in another method, the inks mixed with gold powder were used. These later method was so well improvised, that larger surfaces were painted with it.
For cold gilding, the gold in finely dispersed condition is dissolved in aqua regia (mixture of Nitric and Hydrochloric acids) and applied on the surface by a rag. It is then sintered or lightly burnt, while removing the ash residue.
Gilding is very labourious process, with often uncertain results. Electroplating offers better results. Electroplating can be conducted on electrically conductive materials, these include metals, and coated materials like ceramics or ABS series of plastics. Electroplating is not suitable for wood, unglazed ceramics, ivory, horns and bones, fabrics, paper, leather etc. Gilded items can have many textural effects with controlled or partial or selective area burnishing, whereas for electroplating the only texture that can be made (to the whole item, and not its parts) is reverse plating during the last few moments of the process.
Gold leaf is used for many other purposes. It is used for Ayurvedic (Indian) medicines, as a decorative additive to sherbet. It is used a topping over sweets and puddings. Gold covered or Golden architectural embellishments are used for ceilings, trimmings, glass patterns, stained glass, etc. Baroque period (early 17th to mid 18th C.) show more sloppy gilding practices, but some of the best gilded items were made during early 18th C in France. Sankheda style furniture (Sankheda, Dist. Vadodara, Gujarat, India) using golden ink patterns drawn over coloured shellac base, and covered with clear Lac coatings of different tinges.
Gilding is costly and cumbersome process. It is now being superseded by Golden colour painting. The Golden paints are prepared using Aluminium flakes or powders of golden colours (ranging from light or silvery gold, ‘reddish or ‘copper gold’ or Bronze gold, blackish gold). These are supplied as two-pack system, a varnish (NC Lacquer, polyester resin, alkyd resin, polyurethane or epoxy based) and ready to mix golden paste of flakes or powders. Similar products for water-based systems are available.
Gold covering is also achieved by metallic spraying on glass, plastic sheets and films and aluminium foils. These products are used as protective wrap for space-modules, packing of sensitive electronic goods, solar radiation films, decorative-gift wrapping. Such films and foils are also fixed to utility items for decorative edges or trims. Gypsum and fiber ceilings’ tiles formed with textured patterns are selectively covered by such material creating pseudo gilding effects.