A designer approves a wax that measures exactly US 7 (inner diameter 17.3 mm). The client receives the finished silver ring and it measures 16.9 mm — a half size too small. The factory did not make a mistake. Sterling silver shrinks in two stages, and unless the CAD was scaled up before wax printing, the final piece will always come out small. This article lays out the numbers we use on every silver job.

Two stages of shrinkage

Stage one is burnout and investment. The wax or resin pattern is incinerated at 700–750 degrees C and the ceramic investment sets around the empty cavity. By the time molten silver (925, melting range 890–915 degrees C) is centrifuged in, the cavity itself has contracted slightly. Stage two is solidification shrinkage as the alloy cools. For standard 925 sterling (92.5 percent Ag, balance copper), combined linear shrinkage from wax to finished casting is 1.8–2.2 percent. We design to 2.0 percent as default and adjust after first-piece measurement. ISO 9202 defines fineness; shrinkage behavior is covered in references such as the Sterling silver entry on Wikipedia.

What that means in CAD scaling

A ring the client wants to be 17.3 mm inner diameter at finish must be modeled at 17.3 × 1.02 = 17.65 mm in the CAD. On a printed resin master we use 1.5 percent; on injected wax we use 2.0 percent. The same scale factor applies to outer diameter and overall length — but not to stone seats, because stones themselves do not shrink. If the whole file is scaled 2 percent, the stone seat becomes 2 percent too large and the stone falls out. Our fix is to scale the ring geometry by 2 percent, then cut the stone seat separately to the measured girdle. See 3D-printed wax resolution and fit and lost-wax vs 3D printed wax.

Tolerance stack after casting

Even with correct scaling, downstream steps move the dimension. Sprues are ground off (plus/minus 0.1 mm), the ring is stretched on a mandrel (plus/minus 0.15 mm), stone setting pushes the walls (plus/minus 0.1 mm), and plating adds 2–10 microns (see electroplating thickness and wear). Our working tolerance on finished silver rings is inner diameter plus/minus 0.15 mm and weight plus/minus 5 percent. Deviation outside triggers a re-check on flask temperature, grain, and sprue placement.

Temperature and flask factors

Shrinkage is not a fixed number on every pour. Flask temperature, metal pouring temperature, and cooling rate all move the final dimension by 0.1–0.3 percent. A flask heated to 250 degrees C before casting contracts less than a cold flask because the investment does not shock-crack on contact. Pouring silver at 940 degrees C instead of 900 degrees C extends the liquid phase and increases solidification shrinkage by roughly 0.2 percent. We log flask preheat, pouring temp, and cooling time for every run, and we adjust the CAD scale factor on the second order based on the first batch measured average. This iterative calibration is how we hold ring size to plus/minus 0.15 mm across reorders.

Size adjustment after casting

When a run comes out half a size small, we do not pour a new batch. We stretch the ring on a steel mandrel with a rawhide mallet, adding roughly 0.3–0.4 mm to the inner diameter, standard practice for sizes up to US 9. Above that, and on heavy signets, we laser-weld a bridge and close the gap. Stretching hardens the silver, so we anneal after. We log every adjustment and photograph it for the buyer QC record, as in QC photos before shipment.

Why is my ring smaller than the wax I approved?

Because the wax was not scaled for silver shrinkage. Approve the wax only after the factory has already applied the 2 percent CAD scale. If the wax is exact US 7, the silver finishes near US 6.5.

Does argentium shrink differently?

Germanium-bearing silvers shrink in a similar 1.8–2.1 percent range, but solidifies cleaner with less micro-porosity. We still scale to 2 percent and verify on first piece.

Can I compensate by ordering half a size up?

No — that gives you a ring that is half a size up and 2 percent small, which is unpredictable. The fix is CAD scaling before wax printing.

Got a CAD file that has not been scaled for silver shrinkage? HOLYCOME runs first-piece measurement on every new style and adjusts the scale factor within the first 10 units. Send us your CAD and target ring size — we return a dimensional PDF before any metal is poured.

Frequently Asked Questions

How do I prevent sterling silver from tarnishing in storage?

Use anti-tarnish bags with a sulfur absorber, keep humidity under 60% and avoid paper wrapping. Rhodium plating adds a further barrier on high-turn SKUs.

Is rhodium plating worth the added cost?

Yes for display and gift lines. It resists tarnish for 12–18 months and keeps shelf pieces bright, which reduces markdowns.

What purity do you supply?

925 sterling silver, stamped and hallmarked. Fine silver (.999) is available for beads and bullion-style pieces.

What is the MOQ and lead time?

50 pieces per design, samples 3–5 days, bulk 15–20 days.