Zinc came is made from flat strips of zinc that are then put through a machine that progressively feeds the strip through a series of roll-forms that fold and bend the came into its final shape. When completed, the zinc came has a shape that compares to that of lead came. It is lighter than lead and is hollow. There is a seam on one side of the channel into which the glass fits. In many cases, it is barely discernible.
Although it is lighter than lead, the hollow shape and the mechanical characteristics of the zinc, make it stronger and less resistant to deforming than lead. When bending the zinc came around a curved piece of glass, the seam should, ideally, be toward the edge of the glass. However, this is not always possible when there is a change in the direction of the bend. Zinc will, like a copper tube, tend to kink as you bend it and this can be a problem. For best results, the zinc needs to be annealed before use as it becomes work hardened in the process of roll forming. Great care needs to be used with zinc came because of this characteristic.
In most cases, lead would be the preferred material above zinc came for stained glass windows. The exception would be a fully bevelled glass panel. Here, because of the added weight of the thicker glass, zinc came will be the preferred material. One source suggested that the reason one almost never sees old bevelled glass fabricated with lead came is not that it wasn't used, but that it did not survive. Lead is just too soft to withstand the rigors of the added structural requirements of the bevelled glass.
If you are using zinc came, use 60/40 tin, and lead solder. 50/50 is okay for lead work, because that alloy is stronger than the lead came - this is not so for the zinc. Because of the added weight's potential added stress to the joints, the 60/40 should be used with zinc.
Go and pay a visit to a good studio and ask to see some zinc came. Look at the ends of both the lead came and the zinc came. You will see the hollow core on the faces of the zinc came which is not the case with lead. Notice how the zinc came resists bending in both following a curve around a piece of glass and the resistance to bending against the vertical profile. You will, then, have a better understanding of the strength of zinc came.
Although more expensive than lead per pound, because it is of a lighter molecular weight, you get more strips per pound so that the actual cost per window will be only slightly more than that of lead. With the added structural integrity of the zinc came, it is a very small price to pay for the long term success of the product and your reputation as a glass artist/fabricator.
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