A wholesale brand sends over a CAD spec for a 6 g 14k yellow signet band. The casting room returns finished pieces at 5.4 g and the buyer immediately suspects they got short-weight. In almost every case, that 0.6 g gap is not theft. It is the sum of 2.2 percent linear shrinkage, sprue gates cut off, investment residue removed in pickle, and a few minutes of filing on the bench. Underestimating these numbers is why custom quotes run late, and why buyers and factories argue about gram weight for the first three orders of a relationship.

Shrinkage and weight loss are two different numbers

Shrinkage is dimensional. Every alloy contracts as it cools from pouring temperature to room temperature, and silver casting shrinkage tolerances run around 2 percent linearly in gypsum-bonded investment. Our working table is: brass and bronze 1.5 percent, sterling silver 2.0 percent, 14k yellow gold 2.2 percent, 18k yellow gold 2.3 percent, and platinum around 2.5 percent. The wax room scales every pattern by 1.02 to 1.025 so the casting lands at nominal ring size after shakeout.

Weight loss is financial. Of the metal we actually pour, we recover 88 to 92 percent as finished and returnable scrap. The remaining 8 to 12 percent leaves as sprue buttons which we remelt, investment skin dissolved in pickle, polishing compound embedded with metal dust, and the tiny filings that fall off during bench work. Finished piece weight itself lands within a band, not on a dot: we hold +/-3 percent on cast pieces and +/-2 percent on fabricated pieces, and finished ring weight tolerance is stated on every quote.

Where the missing grams go on a typical run

For a 3-inch flask tree carrying twelve 14k pendants, poured at roughly 120 g of metal, the split usually looks like this: 25 to 30 g of sprue and tree mass that comes back as remeltable button, 2 to 3 g of investment skin removed by pickling and glass bead, 3 to 5 g of gate cleanup and filing, and 1 to 2 g lost to polishing compounds. The pendants themselves finish at 78 to 82 g combined. If you only compare poured metal to finished jewelry weight, you will think the factory kept 30 g of gold. Compare poured metal to finished plus returned sprue, and the number closes.

Porosity changes the math. When 925 silver casting porosity defects show up as voids, we re-flow and re-plate, which adds another 1 to 2 percent of bench loss. We photograph the tree after shakeout so the buyer can see which flask the voids came from before we charge for remake.

How we quote weight before pouring

Three methods, in order of trust. First, CAD volume times alloy density: a 14k yellow crown alloy runs about 13.5 to 14.0 g per cubic centimeter depending on copper content, sterling silver sits at 10.36 g/cc, and fine platinum at 21.45 g/cc. Second, wax weight times the wax-to-metal conversion factor for that alloy. Third, and most accurate, one sample pour measured after finishing. We publish the density factors we use on every spec sheet, and we follow the karat fineness definitions that the marking rules require, so a 14k piece is never rounded up to make weight.

The connection between sprue and investment defects and weight recovery is direct: a badly sprued tree shrinks away more metal in gates it never should have held, and we pass that lesson back to the wax room on every batch.

FAQ: Casting shrinkage and expected weight loss

How much weight is normally lost from casting to finished piece?

Budget 8 to 12 percent of poured metal as sprue, pickle, and bench cleanup. Sprue buttons are returned as remeltable scrap, so the real permanent loss is closer to 3 to 5 percent of the pour. Finished piece weight itself should land within +/-3 percent of the CAD target.

Why is my cast ring 0.5 g lighter than the CAD weight?

CAD volume times alloy density gives a theoretical solid weight. Cast pieces also hold 2 percent linear shrinkage, gate cleanup, and filing, which shave a few tenths of a gram off a 6 g band. If the gap exceeds 0.8 g on 6 g, ask for the shakeout photo.

Does platinum lose more weight than gold?

Platinum shrinks more, 2.5 percent versus 2.2 percent, but its density is 21.45 g/cc, so the absolute gram loss on a comparable piece is larger in platinum. We also cast platinum in phosphate-bonded investment, which we do not remelt the same way as gypsum trees.

How do you price when finished weight varies +/-3 percent?

We quote at nominal weight with a tolerance band and invoice the actual finished gram weight plus a posted scrap buy-back rate for sprue. Buyers who want a fixed price pay the upper side of the band; that is the trade.

Send over your CAD files and target finished weight. Our custom casting bench runs 1 kg to 50 kg per pour, photographs every tree after shakeout, and publishes the density factors and sprue returns on the QC sheet. Small-batch OEM custom manufacturing starts at 30 pieces per design; send the spec and we will quote the weight band before you commit.

Frequently Asked Questions

How do I verify a factory before placing a bulk order?

Request a production video, business license, export records and a paid sample run. A factory that accepts a 50-piece test order is usually a real manufacturer.

What payment terms do you offer?

30% T/T deposit with the balance against the bill of lading. This protects both sides on first orders and can move to net terms after a track record.

What is your normal reject rate?

3–5% under 10x loupe inspection for cast and set pieces. Defective units are replaced free in the next shipment.

Where is the factory located?

Wuzhou, Guangxi, China—the core lab-grown and moissanite manufacturing cluster. Shipments go via Guangzhou or Shenzhen ports.