How to cast resin with embedded objects without bubbles
Embedding objects in clear resin creates beautiful keepsakes, but trapped bubbles can ruin the effect. This guide walks you through a safe, repeatable workflow with practical timings and quantities so your pieces come out clear and smooth.
Step 1: Gather materials and workspace
Set up a clean, dust-free area at room temperature between 70–75°F (21–24°C). Collect epoxy or polyester casting resin (measure 1:1 or 2:1 as labeled), mixing cups, stirring sticks, gloves, a silicone mold, isopropyl alcohol 90%+, a small propane torch or heat gun, a vacuum chamber if available, tweezers, and a scale accurate to 0.1 g.
[Illustration: well-lit table with resin kit, silicone mold, gloves, scale, torch, and tweezers arranged neatly]
Step 2: Prepare and pre-condition objects
Ensure objects are dry and free of dirt; bake organic items like wood or flowers at 200°F (93°C) for 30–60 minutes to remove moisture and outgassing. Seal porous items with 2–3 thin coats of clear acrylic spray, allowing 10–15 minutes dry time between coats to prevent tiny bubbles forming later.
[Illustration: small dried flowers and wooden charms being sprayed with clear acrylic and laid on a tray to dry]
Step 3: Measure and mix resin precisely
Weigh resin and hardener to the manufacturer ratio (for 100 g total at 2:1 mix use 66.7 g resin and 33.3 g hardener). Pour into a clean cup and stir slowly for 3–4 minutes, scraping the sides and bottom for 30 seconds every minute to fully homogenize and reduce entrained air.
[Illustration: hands holding clear cups on scale pouring measured resin and hardener with a stopwatch nearby]
Step 4: Degas mixture if possible
If you have a vacuum chamber, pour the mixed resin into it and pull 25–28 inHg vacuum for 2–5 minutes until the foam subsides; this removes most bubbles before casting. If no vacuum, let the mixed resin rest in a warm place (78–85°F / 25–29°C) for 10–20 minutes to let microbubbles rise and pop.
[Illustration: small vacuum chamber with cup of foaming resin inside, pressure gauge visible at lower reading]
Step 5: Pour in thin layers and embed objects
Pour a 2–5 mm thin base layer and allow 10–20 minutes to level and outgas. Use tweezers to position objects on that tacky layer so they don’t float, then pour additional resin in 5–10 mm layers, waiting 10–20 minutes between layers to let bubbles escape—you want slow fills rather than one deep pour to prevent trapped air.
[Illustration: pouring thin clear resin layer into silicone mold with tweezers placing a small charm carefully]
Step 6: Remove surface bubbles with heat
After each pour, gently pass a propane torch or heat gun 6–8 inches away for 2–6 seconds in sweeping motions to pop surface bubbles—avoid prolonged heat over one spot to prevent yellowing or burning. For delicate items, use a glass droplet technique: touch a warm metal or glass stir stick to the surface to blend and collapse bubbles locally.
[Illustration: person at safe distance sweeping a small torch over a resin-filled silicone mold, torch flame low and controlled]
Step 7: Cure, demold, and finish carefully
Allow resin to cure undisturbed at the recommended temperature for full cure time (typically 24–72 hours). After demolding, remove any flash with 400–600 grit sanding, wash with isopropyl alcohol, then polish with a rubbing compound for a glossy finish. If tiny pinholes remain, fill with thin resin glaze and reheat gently to self-level.
[Illustration: cured resin piece being sanded and polished on a clean bench with polishing compound]
- Work in small batches of 50–200 g to maintain easier temperature control and faster degassing.
- Warm your resin components to 75–85°F (24–29°C) for 30 minutes before mixing to lower viscosity and speed bubble rise.
- Use silicone molds for easier demolding and fewer trapped bubbles compared with rigid molds.
- Place mold on a level surface and avoid walking or vibrating the table during cure to prevent air movement creating new bubbles.
- When embedding very small items, attach them to thin pins or toothpicks first to position without handling the tacky resin.
- If using pigments, pre-mix pigment into a small portion of resin to ensure even color and avoid overmixing which introduces air.
- Keep a damp tack cloth handy to wipe dust off the surface before final pours.
- Record times, room temp, and batch sizes in a notebook so you can repeat successful results.
- Never inhale resin fumes; work in a well-ventilated area or use a respirator rated for organic vapors.
- Wear nitrile gloves and eye protection—wet resin can cause skin irritation or sensitization with repeated exposure.
- Avoid direct, prolonged flame on resin surfaces; excessive heat can yellow the piece and generate hazardous smoke.
- Do not use food containers for mixing resin or storing resin leftovers to prevent contamination.
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