Why Your Finished Piece Is Never Exactly the Same Size as Your Wax Model
If you've ever ordered a cast piece and noticed it came back slightly smaller than your original design, you haven't made a mistake — you've just encountered one of the most fundamental realities of jewelry manufacturing: casting shrinkage. Understanding this phenomenon is essential for any jewelry designer, independent brand, or retailer working with a manufacturing partner to produce consistent, high-quality pieces.
What Is Casting Shrinkage?
Casting shrinkage refers to the dimensional reduction that occurs when molten metal cools and solidifies inside a mold. During the lost-wax casting process, liquid metal contracts as it transitions from a molten state to a solid one. This is a natural physical property of all metals — not a flaw in the process.
The amount of shrinkage varies depending on the metal being cast:
- Sterling Silver: Approximately 4–5% shrinkage
- Yellow Gold (18K): Around 3–4% shrinkage
- White Gold (18K): Typically 3–4%, though alloy composition matters
- Platinum: Generally 2–3% shrinkage
- Brass and Bronze: Can range from 1.5–2.5%
These percentages may seem small, but on a delicate ring shank or a precisely measured bezel setting, even a 3% reduction can affect fit, stone compatibility, and overall aesthetics.
How Shrinkage Affects Your CAD Design
This is where CAD jewelry design becomes an incredibly powerful tool. Experienced CAD designers account for casting shrinkage directly in the 3D model before a single gram of metal is poured. At JewelCAD Design Ltd, our team builds shrinkage compensation into every file — scaling the model slightly larger than the final intended dimensions so that the cast piece arrives exactly where it needs to be.
"A well-prepared CAD file isn't just a pretty render — it's a precision-engineered blueprint that anticipates every stage of the manufacturing process, including how the metal will behave when it cools."
If you're sending your own CAD files to a casting house, always communicate the intended metal and ask whether shrinkage compensation has been applied. Assuming it has — or hasn't — is one of the most common and costly mistakes in custom jewelry production.
Practical Tips for Managing Casting Shrinkage
- Always specify your final target dimensions: Tell your manufacturer the finished size you need, not the size of your model. Let them handle the compensation math.
- Request a wax or resin print proof first: Reviewing a 3D-printed prototype before casting allows you to verify dimensions and catch issues before they become expensive metal mistakes.
- Understand that shrinkage is not uniform: Thicker sections of a piece cool more slowly and may shrink differently than thin areas. Good casting design minimizes dramatic transitions in wall thickness.
- Choose the right sprue placement: Proper sprue positioning helps direct metal flow and supports even cooling, reducing the risk of shrinkage porosity — tiny internal voids that can weaken a piece.
- Work with an experienced casting partner: Metal behavior during casting is part science, part craft. A manufacturer with deep experience in lost-wax casting will already have calibrated their process for predictable, repeatable results.
Shrinkage Porosity vs. Surface Shrinkage
It's worth distinguishing between two types of shrinkage issues. Surface shrinkage affects the outer dimensions of the piece and is managed through scaling in CAD. Shrinkage porosity is an internal defect caused by uneven cooling — it appears as tiny holes or weak spots inside the metal and requires careful mold design, proper alloy selection, and controlled casting temperature to prevent.
At JewelCAD Design Ltd, our Bangkok workshop uses vacuum-assisted casting and carefully monitored flask temperatures to minimize porosity across all metal types, ensuring the structural integrity your pieces deserve.
Getting It Right From the Start
Casting shrinkage is not something to fear — it's something to plan for. When your CAD designer and casting team communicate clearly and work from a shared understanding of how metals behave, the result is a finished piece that matches your vision with remarkable accuracy.
Whether you're a jewelry designer launching your first collection, an independent brand scaling production, or a retailer commissioning custom pieces, partnering with a manufacturer who understands the science behind the craft makes all the difference. Contact JewelCAD Design Ltd today to discuss your next project — we'll handle the shrinkage so you don't have to.