CRACKING AT THE SPRUE JUNCTION ON RINGS MADE
WITH UNITED DEOXIDIZED STERLING SILVER

If cracking is experienced in rings cast with United Deoxidized Sterling Silver alloys exactly on the sprue junction of the cast rings it is usually due to the investment mix being too hard. All precious metal alloys will shrink on solidification and the investment mold must crush slightly to allow for the shrinkage. If the investment mold is too hard it won’t "give" enough on solidification causing the ring castings to crack at the sprue junction being the last area to solidify. The cracks will occur in rings on the shank at the center of the sprue junction. The cracks are often hairline and may not be noticed until inspection of the castings.

To resolve the cracking at the sprue junction problem a higher water ratio should be used in the investment mix. The wetter mix will provide a slightly weaker investment and allow the investment to "give" when the castings solidify. There is some variation between different brands of investment, some are harder than others but most of them can be modified with higher water to powder ratios.

The cracking problem only occurs in ring castings. The use of boric acid additives in the investment to protect gemstones from cracking can cause the investment to be very hard causing cracking at the sprue junction in cast silver rings. CZ’s are normally set in wax with Sterling Silver and won’t require the use of stone casting investment additives.

We welcome your comments and input on this problem.