◆ Concrete
Rainbow arch concrete bookend mold
A heavy rainbow arch bookend, 156 mm wide, to cast in concrete. A silicone mold kit from printed parts.
◆ Concrete
A heavy rainbow arch bookend, 156 mm wide, to cast in concrete. A silicone mold kit from printed parts.
A rainbow arch bookend 156 mm wide, 78 mm tall and 50 mm thick: a solid half disc with three rainbow grooves on its front and a 5 mm round on the front edge, standing on a flat, square base with a flat back for the books. Cast in concrete it weighs about 1070 g, which is what actually holds a row of books up. Cast it twice for a pair.
Made with the hugging-shell mode of our silicone mold maker. The tool suggests a silicone box for this low, wide shape, but its contoured box would take 897 ml of silicone; the shell follows the arch about 10 mm out and takes about 414 ml. The bookend lies on its back, so the back is the face you pour and strike flat, and the rainbow and the rounded edge come off the silicone.
Leave it raw grey, paint the bands in terracotta, sand and sage for the boho look, or cast it in white Jesmonite. The zip carries every printed part, the bookend master as its own STL, the tool's own print-settings sheet and a recipe file for the generator.
Shown as a 3D render of the printed mold parts pulled apart around the master, not a photo.
Print the base, which has the bookend master already fused onto it, the two shell halves and the six clamps (all six are in clamps.stl). No supports.
Stand the base plate on the table, set each shell half down a few centimetres out from it and slide it in until the ridge round the plate sits in the groove at its foot. Push the six clamps over the seams: the shells cannot lift after that, and the ridge seals the bottom.
Tape the outside seams or run a bead of hot glue along them, because silicone finds every gap.
Mix 450 ml of silicone in one batch and pour it into the open top of the shell in a thin stream until it is level with the rim.
Once it has cured, take the clamps off, slide each shell half straight out and peel the silicone off the master. That skin is your mold.
Put the skin back in the shell halves with the clamps on and stand it upside down on the flat top of the silicone. The open face is now on top: it is the flat back of the bookend.
Mix a fine concrete or Jesmonite to a thick pour, brush a thin first coat into the detail, fill slowly down one side, vibrate the shell for a full minute to raise the air, and strike the bookend flat.
Demold after a day: take the shell off and peel the skin back from the rim, a little all round at a time. Let it cure for a week, sand the flat face on paper laid on a board, add felt pads and seal it.
Print details
| Cast material | Concrete |
|---|---|
| Printed parts | 9 |
| Size (W x D x H) | 201 x 124 x 67 mm |
| Print bed needed | 173 x 102 mm, 67 mm tall |
| Filament | ~515 g |
| Layer height | 0.2 mm |
| Infill | 15% |
| Supports | Not needed |
| Download | ZIP: 9 printed parts in 4 STL files + bookend master (STL) + print sheet + recipe |
| Added | 2026-09-27 |
Made with the free Silicone mold maker generator. Upload your own model and get the same kind of mold built around it, in your browser.
Free download. Opens the Thingiverse listing in a new tab.
Free for personal use. Selling the pieces you cast needs a commercial licence (Pro or Founder); passing on the file itself is not permitted on any plan. Full terms.
New to casting? Read the silicone mold maker guide.
Yes for a row of paperbacks, at about 1070 g in concrete: that is more than most shop-bought bookends. For big hardbacks or a long shelf, cast it in a dense mortar mix, or glue a thin rubber or cork sheet under the base so it grips instead of sliding.
Seal nothing yet. Paint each band between the grooves with acrylic or chalk paint, using the grooves as the edge, and leave the grooves themselves grey. Once dry, a matte clear sealer protects the paint from the books rubbing it.
So its back is the pour face: it comes out flat and square from the strike, which is the face that stands against the books, while the rainbow grooves and the rounded front edge come off the silicone smooth. It also keeps the mold low, so the silicone takes less.
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