Friday, 22 February 2013

Process of Chasing and Repousse in Jewelry Making

1 Pitch bowl on support An old heavy saucepan could also be used. It is filled almost to the top with a ready-made pitch mixture;  2 selection of repousse and matting punches.
 Chasing is the art of controlling a small steel tool to push the lines of a pattern along the surface of the metal. The metal itself is not removed, as it would be if an engraving tool were used. Rather, it is moved sideways and compressed downward on the surface of the metal as the tool is pushed along the line. Chasing is used to outline and define areas of metal that have been repoussed, and it is worked from the top, or visible, side of the metal. Repousse is the art of working with punches from the back of an article to form shapes and lines that give your work a three-dimensional appearance when it is viewed from the front.

Type of punches
You will need several different punches for chasing. A tracer punch is used to outline the design. It has a rounded, chisel-type head, which can be rectangular, slightly curved, V-shaped, half-round, and so on. The head is slightly rounded so that the metal is not cut by a sharp edge as the punch is hammered along.

Mark on the metal the area needed for the pattern, making sure that you leave an outside border of 1/2-3/4 inch, then bead down the corners of the metal with a pair of flat-nosed pliers.
A modeling punch has a flat, rounded head, and it is used to define areas of repoussed work by pushing down the metal around and between the raised areas. Keep the head rounded and shiny so that the metal is not marked when it is being worked.

A matting punch has a patterned head and is usually used to punch texture into background areas. Matting punches also vary in shape and size, and the faces of the heads can be crisscross, striped, lined or dotted, but, like the other punches, the heads should have rounded edges. The patterned faces are not polished, because this would lead to loss of definition.

A planishing punch has a polished, flat face. These punches, which are made in a range of sizes, are used for smoothing over repousse marks left by the punches used to work the back of the metal.
Circles in relief are made by a hollow-faced punch, which can be used on either the front or the back of the metal. The heads of these punches vary in diameter, and, as with matting punches, they are not polished so that definition is not lost. The edges are slightly rounded so that the metal is not cut by the punch.

Heat the pitch until runny and shiny, then place the metal in it. The turned-down corners, or tabs, will help to hold the metal firmly. Wet the ends of your fingers and push the pitch over the edge of the metal.
Most repousse work is done with an embossing punch, which is used to push up areas of metal from behind to create the relief on the front. These punches are usually oval, round, square, or rectangular, and they have rounded edges and polished faces.

Using punches
When you use a tracer punch to make a line, the top of the punch is held at a slight angle away from you, while the bottom or face is toward you so that the line being traced is clearly visible. Hold the punch between your thumb and three fingers, while your little finger rests on the metal to steady and support your hand. Hit the top of the punch rhythmically with a chasing hammer a small hammer with a broad head and a well-balanced handle which facilitates repetitive hitting. If you are using a tracer punch to outline a curve or a V-shape, hold the punch upright and give it a single hammer blow.

When the pitch is cool, rub the surface of the metal with modeling clay or putty and trace the pattern through the tracing paper to the surface of your work.
Modeling and planishing punches are held in the same way as the tracer punch, and they, too, are hit with the chasing hammer.

Matting and hollow-faced punches are held upright and struck with a single hammer blow. The punch is then lifted and repositioned on the metal so that it slightly overlaps the previously punched area.

Embossing punches are held slightly away from you and hit continuously. The punch is moved across the metal and not lifted from the surface in order to form a smooth, indentation in the metal.

Holding your work
Tap the head of the tool with gentle, rhythmic strokes with a chasing hammer while following the line.
Work that is going to be chased and repoussed has to be held in a firm but "giving" medium called pitch, which is a mixture of pitch, tallow or linseed oil, and plaster of Paris or pumice powder. You can add tallow or linseed oil to pitch to soften it if it becomes brittle, which sometimes happens in cold weather.

Metal will be held more firmly in the pitch if the corners of a piece are turned down. Allow a good margin around the design so that you can turn down the corners with pliers.

Use a file to clean up the edges before polishing the piece.
You will have to take the metal from the pitch several times during the chasing and repousse process. Not only will it need annealing from time to time to keep the metal pliable, but you will have to turn it over when you have to work on the back or the front. When you remove the work, gently heat the pitch around the metal and lift up one corner with an old pair of insulated tweezers. The metal will be covered in pitch, and you have to remove this before you can continue with your work. Hold the work in the flame of your torch so that the pitch burns off. Allow the pitch to burn until it is dry and forms flakes, which will either fall off or can be blown off. Do not quench the metal until the pitch has burned off. This method also anneals the metal.

When you put the piece back in the pitch, the indentations on the back need to be filled with pitch to provide support. The piece would collapse if a matting, tracing, or planishing punch were used on unsupported metal. Keep a small, separate container of pitch and heat it up so that you can pour it into the indentations. Allow it to cool before turning the piece over and replacing it in the pitch.

Writer – Jinks McGrath

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