How to make a cast of any object

To make a cast of an object, you need a mold of it — and the easiest mold for almost any shape is silicone. With a 3D printer, the process is: get a 3D model of the object (download, design or scan it with your phone), print a master and a mold box, pour silicone around the master, then cast copies in resin, plaster, wax or concrete. Here's each step, including what to do when the object can't be scanned.

Step 1 — Get a 3D model of the object

There are three ways to get the STL file you need:

• Download it. If the object is a known shape — a figurine, a part, a decorative piece — there may already be a model on a model-sharing site.
• Make it without CAD. Many objects people want to cast — trays, nameplates, stamps, planters — can be generated from numbers or text in the browser; see how to make 3D-printable models without CAD.
• Scan it with your phone. Photogrammetry apps turn a series of photos into a 3D model. Free tiers and export formats change often, so check before you start that your app can export a mesh format such as STL or OBJ on the plan you use — some only export other formats for free.

Step 2 — Scan well (if you're scanning)

• Pick a scannable object. Matte, rigid objects with some surface detail — roughly fist-sized to breadbox-sized — scan best. Shiny, transparent, very dark, fuzzy and very thin objects scan badly.
• Tame shiny surfaces with a light dusting of a removable powder or a scanning spray.
• Light it evenly — bright overcast daylight, or lamps bounced off a white wall. No flash.
• Overlap your photos. Walk around the object in rings at low, level and high angles with lots of overlap between shots; capture the underside in a second pass.
• Keep a ruler in frame so you can set the real size later.

Expect a phone scan to be accurate to a few millimeters — great for decorative casts, not for parts that must fit precisely.

Step 3 — Clean up the scan

A raw scan is a skin, not a solid. Before it becomes a master:

1. Crop away the table and floating fragments.
2. Close the holes so the model is watertight — most scanning apps or a free mesh tool can do this.
3. Set the scale using the ruler or a measured dimension, and check a second dimension.
4. Reduce the triangle count if the file is huge.

Then scale or resize the STL to the size you want the casts to be.

Step 4 — Build the mold box

You can draw a mold box in CAD if you have the time, but I use the 3DGEN silicone mold box generator — upload the STL and the printable box is ready in seconds in the browser, no CAD.

1. Upload the model and orient it with the rotate controls so its flattest side sits on the base — that side becomes the opening of the mold. The generator runs a basic repair on upload (welding vertices and fixing flipped faces), but large holes still need closing beforehand.
2. Choose the box shape — Rectangular or Round — and set Silicone wall thickness and Top margin (over model).
3. Choose how the master sits on the base under Registration: a pin and socket, or merged to the base.
4. Click Build the box and read the Material estimate panel — it shows how much silicone the box will hold.

Print the master smooth — silicone copies every layer line — and print the box so its seams seal.

Step 5 — Pour the silicone

• Test first. Some materials stop platinum silicone from curing; dab a little on the master and let it cure. Tacky? Seal the master — see why silicone won't cure.
• Mix by weight at the ratio on the data sheet, scraping the cup.
• Pour in a thin stream into a corner of the box and let it rise over the master.
• Cure fully, open the box and pull the master out. The silicone mold is reusable.

Step 6 — Cast your copies

Pour your casting material into the silicone mold: epoxy resin for clear or colored copies, plaster or jesmonite for stone-like pieces, wax for candles, concrete for heavy decor. Follow the material's own mix ratio and cure time, tap out bubbles, and demold once it has set. The step-by-step for each is in how to cast resin at home and how to cast jesmonite.

If you can't scan the object

Some objects won't scan — glass, chrome, very fine detail. You can still mold the real object the traditional way: fix it to a flat base, build a simple box around it (plastic sheet, LEGO bricks or foam board, sealed at the seams), check the object is sealed and safe to coat, and pour silicone over it. You lose the convenience of a generated box, but silicone copies the real surface directly.

FAQ

Can I make a mold of any object?

Almost — silicone captures nearly any rigid shape. The limits are objects that silicone would damage or stick to, and deep undercuts that trap the mold; a flexible silicone mold handles mild undercuts.

Do I need a 3D scanner?

No. A phone photogrammetry app is enough for decorative objects, or you can download or generate the model instead.

How much silicone do I need?

Build the box in the silicone mold box generator and read the Material estimate panel, or work it out by hand with this guide.