Jewelry Casting: Master Dimensional Accuracy with the Castable Resins for jewelry

Castable Resins: Dimensional Accuracy, Shrinkage, and Metal Shrinkage Calculation.

In jewelry, dimensional accuracy is one of the most critical characteristics for castable resins. Early castable resins suffered from a defect known as post-printing shrinkage, which caused a continuous and constant contraction over time after the print was completed. This phenomenon was virtually uncontrollable because no definitive changes could be made to the printing parameters, as the shrinkage was ongoing: essentially, UV cross-linking continued even inside the printed part.

Today, R&D departments have worked intensely to resolve this issue. However, post-printing model shrinkage is not the only factor; the following stages must be considered globally:

Phase 1: Shrinkage during printing
Phase 2: Post-printing shrinkage
Phase 3: Metal shrinkage during the casting phase

Phase 1 - Shrinkage during printing

The process of cross-linking and hardening of the resin triggered by a UV source causes molecular chains to form and compact. In this phase, a shrinkage between 0% and 2% is expected. High-quality castable resins, such as X-One v2, X-Wax, and X-Wax Filigree, typically have a shrinkage between 0.5% and 1% only (assuming accurate and correct polymerization times).

This type of shrinkage is easily controlled by the printing parameters in the slicing software. Taking Chitubox as an example: if the shrinkage refers to the entire model, simply go to SETTINGS -> ADVANCED -> SHRINKAGE COMPENSATION and increase or decrease the percentage value according to the variations between the printed model and the digital model. If the shrinkage only affects details, such as prong tips, you must instead use the Tolerance Compensation values in the advanced options panel. Increase values A and B if the model details are smaller than intended; conversely, if the details are larger, set A and B to negative values (using the minus sign), always following precise measurements of the parts.

Phase 2 - Post-printing shrinkage

This is the most difficult phenomenon to compensate for. If low-quality castable resins are used, it will be almost impossible, as the shrinkage is continuous and will not stop even after prolonged UV post-curing. In the case of BlueCast X-One v2 / X-Wax / X-Wax Filigree (D iscover More), this phenomenon is virtually 0% and can reach a maximum of 0.5% only after massive UV curing. For all resins, it is recommended to perform a dimensional check after a 10-minute UV treatment and adjust the SHRINKAGE COMPENSATION in Chitubox accordingly. Usually, a resin with high post-printing shrinkage is made with volatile monomers that are potentially hazardous to human health.

Phase 3 - Metal shrinkage during the casting phase

In this phase, we must distinguish between two moments:

Solidification Shrinkage: The crucial transition from liquid to solid. "Shrinkage porosity" can form here if the metal is not properly fed. While not the main focus of this article, it is sufficient to use adequately sized sprues that "stiffen the model," avoiding excessive distances between the metal entry point and the end of the model. If you want discover more how to properly prapere a casting tree you can take a look to this video: Prepare a casting tree
Solid Shrinkage: Occurs from the moment the metal is solid until it reaches room temperature. This is the shrinkage that must be accurately calculated for the final dimensions of the piece.

Average shrinkage for common noble alloys:

Gold (Jewelry alloys): 1.2% – 1.5%
Sterling Silver (925): 1.5% – 2.0%
Platinum: 2.5% – 3.0%
Brass / Bronze: 1.5% – 2.1%

Other factors affecting shrinkage:

Casting Temperature: The higher the temperature of the metal relative to its solidification point (superheating), the greater the total shrinkage.
Model Geometry: Pieces with less mass or very thin walls cool faster and may show different deformations compared to massive pieces (such as commemorative rings).
Water/Investment Ratio: Using a 36-37/100 mix instead of 40/100 reduces the expansion of the investment and simultaneously makes it more solid, limiting the alloy's shrinkage.

X-WAX / X-One and X-Wax Filigree: 0 shrinkage

The new BlueCast castable resins have been developed to automatically counteract and compensate for shrinkage by "expanding" during the investment preparation phase, absorbing water from it. However, the model must be prepared correctly and certain rules followed to ensure shrinkage and expansion are balanced.

During the washing process, alcohol penetrates the models, removing part of the uncured resin and making them more hygroscopic. Specifically, the alcohol removes surface monomers and slightly softens the outer structure, creating more "molecular space" for water absorption from the investment.

Models washed for 4–5 minutes maintain precise dimensions. The longer the washing time, the more the models tend to absorb water later (during investment). The more massive the models, the less pronounced the expansion will be; therefore, washing times are more relevant for lighter, thinner models. You can find out where to buy BlueCast resins at this link: Where to buy

Suggested washing times:

3 minutes for thinner pieces
5–6 minutes for standard models
10 minutes for heavier models (commemorative rings)

The water percentage in the investment is also key: a 40/100 ratio amplifies the effect, while the best results are obtained with a 36–37/100 mix, which also ensures better performance of the investment material.

Final Suggestion: If you need to cast immediately after washing, always perform a 5-minute UV cycle to stabilize the model and evaporate excess alcohol. If casting the next day, you can skip this step. My advice is to test a procedure and adopt it as a standard workflow: short washing time, 5 minutes of UV curing, 36–37/100 water ratio, and adjust compensation tolerances only if necessary.

FINAL CONSIDERATIONS

The simplest path is to standardize the production cycle: from washing the model to preparing the investment, through to casting temperatures and flask cooling times. Cooling too rapidly (e.g., quenching in water too early) can cause stresses that alter dimensions or create micro-fractures.

Using high-quality resins that eliminate post-printing shrinkage is fundamental. That said, measure and verify the dimensions of the cast piece and only then modify the slicing compensation parameters. Only by doing so will you achieve perfect and consistently accurate models.