_{Written by Daniel Mariotti}

_{Photos and Graphics by Daniel Mariotti}

Artists who transform their work into bronze might be surprised to learn that the final sculpture is slightly smaller than the original. This bronze shrinkage happens naturally during the casting process. Let’s explore why it occurs and how it plays a role in both art and conservation.

The Casting Process and Bronze Shrinkage

Most sculptures begin as an original model, often made in clay. To cast it in bronze, the artisan first creates a mold that captures every detail. Then, hot liquid wax is poured into the mold to form a wax version of the sculpture.

Here’s where shrinkage starts. The wax is at its largest while it’s hot, but as it cools, it contracts slightly and pulls away from the mold. Even small factors, like the temperature of the wax, can affect how much it shrinks. By the time the wax sculpture is cooled, it’s already a little smaller than the clay original.

From Wax to Bronze

Next, the wax sculpture is coated in layers of liquid ceramic to form a hard shell. This shell, sometimes called a “waste mold,” doesn’t expand or contract. Once the ceramic shell is complete, it’s fired in a kiln to burn out the wax, leaving behind a hollow space.

The final step is pouring molten bronze into the shell. Like the wax, the bronze is at its largest when it’s hot. As it cools, it shrinks again, sometimes cracking the ceramic shell as it contracts. When the bronze has fully cooled, the shell is removed, and the artist is left with a slightly smaller version of the original sculpture.

How Conservators Use Bronze Shrinkage

Shrinkage may sound like a minor detail, but it actually helps art conservators. Experts can use the slight size differences between sculptures to determine whether a bronze is an original, a first-generation recast, or a later copy.

Recasting is common and often done with permission from the artist or their estate. Authorized recasts usually come from molds taken directly from the original and are part of a limited edition.

However, unauthorized copies can be made from re-casts of re-casts, and so on. These are made by molding existing sculptures or by sculpting from photographs instead of the original mold. Each time a copy is recast, the sculpture shrinks and loses detail, making it easier for experts to spot later versions.

Why It Matters

The science behind bronze casting may seem small, but it makes a big difference. Whether you’re an artist, a collector, or just curious about the process, understanding why bronze sculptures shrink adds a deeper appreciation for the craftsmanship and history behind these works of art.