Painting on Glass and Porcelain. (III)

Manufacturer and builder 11, 1876

Continued from page 183.

We will firm describe the manner of proceeding to decorate hard porcelain, that is, such as is composed of kaolin, and which is considered the best, as indeed it in. The preparation of the colors and the way of using them is however nearly the same for this porcelain as for the softer qualities — the enamelled earthenware and the fine quality of the some inside of pipeclay. The composition of the colora differs only in regard to the amount of flux they contain, that means that their fusibility must he in accordance to the nature of the pieces to be decorated and of the degree of heat they can stand. In hard porcelain the difference between the fusibility of the glazing or enamel and that of the color, may be considerable; for the softer kinds of porcelain and earthenware it should be nearly the same; in the last case it is a real advantage, because the colors penetrate, and, as it were, identify themselves with the objects.

The preparation of the colors requires great care; they are in commerce designated as vitrifiable colors and porcelain colors, and are generally (add in the form of a fine impalpable powder. They must however be ground over again on the ground glass with very pure water, until they no longer produce any grating sound nor feel gritty under the fingers; the water is evaporated, and they are then placed on the porcelain palette after having mixed them with the end of the tempering knife with a little ordinary spirits of turpentine.

In order to perform this grinding operation properly, it is well to first clean the glass plate with a linen rag and a little alcohol; it is also well to spread over the glass from time to time it little wool ashes, in order to remove all greasiness. Care must be taken to rub round and round, so as to bring the color alwap back to the center, else to scrape the color to the middle with the palette-knife, and to rub again, applying more pressure.

Colors thus prepared dry without becoming pulverulent, and can be perfectly preserved. Small amount, can afterward be taken in quantities sufficient for the wants at the moment it is to be used; it is then mixed with a little more turpentine, and in case of necessity, a very little thick lavender oil, until it has the consistency of a thick syrup. The degree of this consintency depends on what is to be painted, and it is only by experience that one learns the right degree of consistency needed. We must add however that in is case must the color be made too thick, notwithstanding it given greater facility in painting, because when too thick it may cause cracks in the paint, which leaves the white of the porcelain visible between them.

Before commencing the work, the artist must know his colors, end for this purpose it is necessary that he should make a series of samples on the same kind of porcelain he is going to decorate. An excellent way to do this is to apply to a palette, or what is better, to a square, tile, vertical and horizontal bands ¼ inch wide, and leave between, the bands an equal space, and applying the colors in the same order; in this way may be seen, not only the effect of the baking upon a single color, but also how it acts upon various mixtures, as by this way of proceeding every color passes successively over every other color, and this is very important. There are in fact certain colors which must never be mixed; such are the colors derived from gold, with those derived from iron, which spoil the brilliancy of the gold colors, or certain delicate colors with others less delicate; they are "devoured" — such is the technical term — by the latter, and the inspection of the painted tile will teach which are the more or less delicate.

The specimens of the isolated colors are also very useful. In making them it is well to put the color on with a large brush, and to apply it in layers in various degrees of thickness, no as to obtain graduated tints. When employed in too thick layers, certain colors peel off and do not adhere to the enamel of the porcelain, when too thin, they do not resist the action of the fire, and sometimes disappear almost completely. At first sight such a preparation of samples may seem extravagant, but all experts in this business agree that it not only cannot be too strongly recommended, but also that the samples should be made with care; the result is a great saving in mistakes and touches which may spoil the objects. A good porcelain painter never uses a color without having first tried it in the way described, so as to learn exactly how it behaves in the fire, as well as its mixture with other colors. Even with the help of these samples, making them with the utmost care, it will often happen, especially in the beginning, that disagreeable surprises will come from the furnace. It is only by long continued practice that the colors become well known, and that the artist her sure of the results of their employment.

Ei kommentteja :