Benefits of opaque porcelain layer.. Bonding the metal structure

Benefits of opaque porcelain layer:
a- Bonding the metal structure.
b- Initiating the color.
A- & b. ***

Bonding is one of the first assembly techniques of a structure that Man has used in addition to that of the wedge for fitting.
Another technique, just as old, was to perform a ligature on a wooden handle, bone or horn, links are usually deer tendons.
The attraction for collage is not fortuitous, it must be pointed out that nature has always been particularly generous, since at all times and in all places, it has made available to Man a large number of natural adhesive products of vegetable, animal and mineral origins such as glue extracted from the soft bark of holly, the viscous flesh of mistletoe fruit (used by Romans to trap small birds), pressed garlic clove juice (used at the beginning of the twentieth century by lunetiers to perfect the maintenance of glasses in their mount), gum arabic extracted from several varieties of acacias, such as Senegal Acacia, also called gum, (gum arabic is the main component of the pastille Valda®, which, as we know, sticks to the teeth and is quite capable of inducing unwanted loosening of a dental prosthesis), the latex drawn from certain rubber species from which the rubber is drawn, as a base number use glue, coniferous resin sap, cereal flours, charcoal tar, betulin (birch pitch obtained by calcination of the bark of the tree, which was used to repair broken ceramics and glue the flint blades of the first tools in the West), white and egg yolk as well as honey (used in the Middle Ages and early Renaissance to bind the colored pigments and paste the gold leaf on the manuscripts illuminated), shellac secreted by certain species of mealybugs, beeswax (used to waterproof the first ceramics and for seals), milk casein (used at the beginning of the twentieth century in the nascent aeronautics), bitumen (fossil mineral natural substance that is usually found in sedimentary basins) used very early in parallel with betulin to paste the first tools), etc., the examples are not lacking.
Before humans, some animal species have used and still use collage techniques to ensure their survival. Examples include spiders that coat some threads with their web to trap the insects they feed on. Let us also mention the case of the mussels which solved their fixation problem, on the rocks and on the bouchots, in conditions that we describe today as technologically difficult, namely in aqueous and saline environment: the byssus is composed of a protein secreted by the animal, which is organized into a bundle of silky filaments that adhere to the supports by electrostatic interactions. At the present time, it is known to prepare the protein by genetic engineering, and the medical and dental environments are very attentive to the solutions that this protein can bring to the problems of adhesion and suture in surgery. Among the many "stuck" marine invertebrates are the barnacles (Figure 1) which are small pyramidal crustaceans 2 to 3 mm high, found on mussel and oyster shells, on rocks and unfortunately also on the hulls of boats to the chagrin of boaters, whose fixing is ensured by means of a cement resulting from the polymerization of molecular elements (heptapeptides) by the intervention of an enzyme called phenol-oxidase, secreted by specialized glands of the animal.
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