cements, glass to metals - Cements, Glass to Metals; cements, glass to metals -
A cement of great adhesive property, particularly serviceable in attaching the brass mountings on glass lamps, as it is unaffected by petroleum, may be prepared by boiling 3 parts of rosin with 1 part of caustic soda, and 5 parts of water, thus making a kind of soap which is mixed with ½ of its weight of plaster-of-Paris. Zinc white, white lead, or precipitated chalk, may be used instead of the plaster, but when they are used the cement will be longer in hardening.
A cement for such purposes as fixing metal letters to glass windows consists of copal varnish 15 parts, drying oil 5 parts, turpentine 3 parts, oil of turpentine 2 parts, liquefied marine glue 5 parts. Melt in a water-bath, and add 10 parts dry slaked lime.
Brass letters may be securely fastened on glass windows by the following recipe:
Mixed just before using, this forms a quick drying and secure cement.
1 lb. of shellac, dissolved in a pint of strong methylated spirit, to which is to be added 1/20 part of a solution of indiarubber in carbon bisulphide.
Take 2 oz. of a thick solution of glue, and mix with 1 oz. of linseed-oil varnish, or ¾ oz. of Venice turpentine. Boil together, agitating until the mixture becomes as intimate as possible. The pieces cemented should be fastened together for a space of 48 to 60 hours.
One of the best cements for uniting glass to other substances is prepared by putting the best and purest gum arabic into a small quantity of water, and leaving it till next day, when it should be of the consistence of treacle. Calomel (mercurous chloride or sub-chloride of mercury) is then added in suitable quantity, enough to make a sticky mass being well mixed on a glass plate with a spatula. No more is to be made than that required for immediate use. The cement hardens in a few hours, but it is wiser to leave it for a day or two. To ensure success it is necessary to use only the very best gum; inferior sorts are absolutely useless.
Before glass can be soldered to metal, it must be "quicked" upon the side that is to be soldered. The "quicking" process is similar to, if not identical with, the method of silvering looking-glass. When the glass is quicked, it may be readily soldered to the metal, using Venice turpentine or chloride of zinc as a flux.
60 parts starch, 100 finely pulverised chalk, are made into a mixture with equal parts of water and spirit, and the addition of 30 parts Venice turpentine, taking care to agitate the mass with a stick, so as to ensure its homogeneity.
4 parts glue melted with the least possible quantity of water, 1 part Venice turpentine; will resist moisture.
That solder in some form adheres to glass is well known and practised by the makers of fictitious jewellery. These are made up of pieces of black glass, cut and polished, and fairly soldered on to metal plates. By breaking one of these across, it will at once be seen how strong the adherence really is. If the work has been well done, the pieces of glass do not fly off, but are difficult to remove except in fragments. This soldering is done as follows: The shields, or metal plates, are coated with a thick layer of tin; these, together with the appropriate pieces of glass, are laid on an iron plate, heated to the melting point of the tin. The piece of hot glass to be soldered is then picked up with forceps, and its edge introduced under the surface of the melted stratum of tin, and slid forward so as to carry some of the metal before it, thus skimming off the oxidised surface so as to bring clean glass and clean metal in absolute contact. No glue must be used; the least trace of oil or resin will spoil the operation. When the piece of glass is fairly in place it is pressed down in order to squeeze out the surplus solder. It is this sliding action that ensures success; if the glass were to be directly pressed down upon the tin solder, no adhesion would take place at all, from the presence of a trace of oxide and the existence of an air film. The glass, of course, must be polished and perfectly clean. (F. H. Wenham.)
Wiederhold recommends a fusible metal, composed of 4 parts lead, 2 parts tin, and 2½ parts bismuth, which melts at 212° P. The melted metal is poured into the capsule, the glass pressed into it, and then allowed to cool slowly in a warm place.
Cailletet describes a process of soldering glass and porcelain to metal. The glass tube to be soldered is first covered with a thin coating of platinum or silver, by treating it with a film of platinum chloride or silver nitrate, and heating to dull red. A ring of copper is next electro-deposited on the platinised tube, which can then be soldered like any ordinary metallic tube. Solderings effected in this manner are said to be very strong. The top of a tube attached to Cailletet's apparatus for liquefying gases terminates in a soldered end and successfully resists pressure over 300 atmospheres.