Absolute cleanliness is the secret of successful soldering. Polish with steel wool the metal surfaces to be joined, the tip of the soldering iron, and the solder itself. Heat the iron until it is hot, but never red hot. Hold the tip vertically on a cake of sal ammoniac and apply solder to the tip until it is coated. This is known as tinning the tip.
Now coat with flux both of the metal surfaces which are to be joined. Dip the tip of the hot iron in a little flux to clean it and apply it to one of the prepared areas. When the metal has been heated, touch a little solder to the tip. It will melt and adhere to the fluxed surface. Treat the other piece of metal in the same way and allow it to cool.
When you are ready to join the two pieces, place a little flux again on each and hold them together in the proper position. Reheat the iron, dip it in flux and press the tip on the upper piece of metal or on the joint itself. As soon as the solder begins to melt, remove the iron and hold the pieces together until the joint is firmly set.
While this method of soldering may be used in most instances, you will find that some metals require special treatment. A hard solder must be used with nickel silver, whereas a very toft solder and low heat are advisable for pewter. Aluminum is difficult to join unless a special solder made for the purpose is used.
While shallow bowls can be shaped most easily in hollow molds of the type described above, they may also be hammered over rounded stakes of metal or hard wood. The technique requires more skill, but has the advantage of making possible a great variety of forms with very simple equipment (fig. 99).
b. The rounded end of a small baseball bat held upright in a vise provides a good stake and can be made to curve a rim to almost any shape; it will also handle work in a wide range of sizes. The metal should be hammered over the stake with a round-faced wooden mallet. If a flat-faced mallet is used the striking surface should be covered with leather. Hit the metal just beyond its point of contact with the stake and draw the blow toward you at the moment of impact. A stake of this kind is also useful in removing kinks and folds from the edges of objects formed on a hollow mold.
Square or rectangular objects, such as the tray illustrated, can be hammered over a mold made by nailing two strips of half-round molding to a bench at a 90° angle. The corner joint should be tightly mitered. In hammering, hold the metal level and work around the edges gradually, turning the tray frequently (fig. 100).
When you have finished any of the above projects, you may wish to bring the surface of the article to a high polish or modify the color of the metal to some extent. The easiest method of hand polishing is to rub the object with a very fine grade of steel wool. Used with linseed oil, a softer effect can be obtained. The final work may be done with buffing powder and a chamois.
The colors of all the craft metals except pewter and tin may be darkened and mottled by the application of heat. The change is caused by oxidation and is particularly noticeable in copper. The article is held in a pair of pliers and passed through the blue flame of gas or a Bunsen burner until the desired color is reached.
Various acids will also produce oxidation. In mixing, always put the water in first and add the acid gradually. A weak solution of muriatic acid rubbed on pewter, aluminum, or tin plate will produce a beautiful dull-gray finish. A similar effect can be obtained on these metals by applying a little powdered graphite mixed with linseed oil and polishing with fine steel wool. Copper and brass can be darkened with a solution of potassa sulphurata (about 1 teaspoonful of acid in 4 ounces warm water for copper; a stronger mixture for brass). Apply with a rag until the desired color is reached. Rinse the article in warm water and dry.
Copper may also be given an antique green or verdigris color by immersing for an hour or more in a solution composed of 1 quart water, one ounce sal ammoniac and three-fourths of an ounce common salt. When it shows signs of cha jing color, remove it and allow it to stand over night without drying. Then wipe with a soft cloth and polish with wax. The verdigris color will not show at once, but will appear in the course of the next few days or weeks.
When a metal object has been finished, its surface must be protected from the slow oxidation caused by the action of the air. The easiest method is to clean the metal with steel wool, apply a coat of prepared floor wax and polish with a soft cloth when the wax is dry. Metal lacquer provides the greatest protection, but is difficult to apply.