Preserving a spider in resin takes about a week of preparation and a day or two of casting, with the drying stage being the most important part of the process. Skip it or rush it, and you’ll end up with a cloudy, shrunken, or discolored specimen trapped in an otherwise clear block. Done right, resin preservation produces a crystal-clear display piece that lasts indefinitely.
Why Drying Comes First
A spider’s body is mostly water, and resin doesn’t mix with moisture. If you embed a fresh specimen directly, the trapped water will cloud the resin, create bubbles, and cause the spider’s abdomen to collapse or discolor over the following weeks. You need to remove virtually all the moisture before the spider goes anywhere near resin.
The two most accessible methods are silica gel desiccation and freeze drying. For silica gel, place the spider in an airtight container buried in a generous bed of silica gel crystals (the same packets you find in shoe boxes, but bought in bulk). An average-sized spider takes roughly 5 to 8 days to fully dry this way. Larger species with bulky abdomens may need longer. Check every couple of days by gently touching the abdomen: it should feel firm and papery, not soft or spongy.
One common problem is abdominal collapse. The thick body fluids inside a spider’s abdomen can cause it to shrivel as moisture leaves. If this happens, you can reinflate the abdomen with a tiny ventral injection of deionized water, refreeze it immediately with a canned freeze spray, and restart the drying process. This is fiddly work, so using a fine-gauge syringe and a steady hand helps.
Positioning the Spider Before Drying
Once a spider is fully dried, its legs become rigid and brittle. That means you need to pose it before or during the early stages of drying, not after. If you want the legs fanned out in a natural stance, arrange them while the spider is still pliable (freshly dead or freshly thawed) and pin them in place on a foam board. Then place the entire pinned setup into your drying container. When drying is complete, the spider will hold that pose permanently.
If you’re working with a spider that’s already dried in a curled position, you can relax the legs by placing it in a sealed container with a damp paper towel for 24 to 48 hours. The humidity softens the joints enough to reposition them. Pin them in the desired pose and dry again.
Choosing the Right Resin
Not all resins work equally well for biological specimens. You want a clear casting resin that cures slowly and generates minimal heat. Epoxy resin is the most common choice for beginners because it’s forgiving and produces excellent clarity. Polyester resin cures faster but releases more heat and has stronger fumes.
Heat matters because resin generates warmth as it cures (an exothermic reaction). In a thick pour, this heat can build up enough to yellow the resin, warp the mold, or effectively cook the specimen, turning a golden-brown spider into a dark, shriveled blob. Thin pours in layers solve this problem, which is exactly what the embedding process requires anyway.
The Layered Embedding Process
Casting a spider in resin is done in stages, not all at once. The goal is to suspend the spider in the center of the finished block so it appears to float. Here’s the sequence:
- First layer: Mix your resin and hardener according to the product’s ratio, then pour a thin base layer into your silicone mold. This layer should fill roughly one-third to one-half of the mold depth. If your mold is face-down (as most cube and dome molds are), this base layer becomes the top of your finished piece.
- Partial cure: Let this first layer set for about 60 to 90 minutes, until it reaches a gel-like consistency. It should be firm enough to support weight but still slightly tacky. If you wait too long and it fully hardens, the next layer may not bond cleanly and you’ll see a visible seam line.
- Place the spider: Gently set the dried spider onto the partially cured layer. Because the resin is already gelled, the lightweight specimen won’t sink or float. Use a toothpick or tweezers to adjust the position and make sure legs aren’t folded under.
- Final pour: Mix a fresh batch of resin and pour it slowly over the spider, filling the mold to the top. Pour from the side of the mold rather than directly onto the specimen to avoid displacing it or trapping air under the legs.
Some people add a colored or opaque backing layer at the very bottom of the mold before starting. A thin layer of tinted resin (black, deep blue, or white) gives the spider a contrasting background that makes details pop, especially for lighter-colored species.
Dealing With Air Bubbles
Bubbles are the most common frustration in resin casting. They form during mixing, get trapped under spider legs, and rise from tiny crevices in the dried specimen. A few techniques help. First, stir your resin slowly and deliberately rather than whipping it. Fast stirring introduces air. Second, after pouring each layer, pass a heat gun or small butane torch quickly across the surface. The brief warmth pops surface bubbles without overheating the resin. Hold the heat source 6 to 8 inches away and keep it moving.
For bubbles trapped beneath the spider’s body or between its legs, a toothpick can coax them free while the resin is still liquid. Pressure pots offer the most reliable solution for serious casters: placing the filled mold inside a pressure pot at around 40 to 60 PSI compresses any remaining bubbles to an invisible size.
Curing and Demolding
Full cure time depends on the resin brand and ambient temperature, but most epoxy casting resins need 24 to 72 hours to harden completely. Warmer rooms speed the process, cooler rooms slow it. Don’t rush demolding. If the resin still feels slightly soft or warm, give it another day. Pulling a partially cured piece from its mold can leave permanent dents or fingerprints in the surface.
Once demolded, you may notice the surface is slightly cloudy or has minor imperfections. Wet sanding through progressively finer grits (starting around 400 and working up to 2000 or 3000) followed by a plastic polish restores full optical clarity. This finishing step takes patience but transforms a decent casting into a truly glass-like display.
Safety While Working With Resin
Uncured resin is a skin sensitizer, meaning repeated exposure can trigger an allergic reaction that gets worse over time. Once you’re sensitized, even brief contact can cause rashes, swelling, or breathing problems. Nitrile gloves are the minimum for every pour and mixing session, as latex gloves don’t provide adequate protection against epoxy.
Eye protection matters too, since a splash of hardener in the eye is a medical emergency. For ventilation, work in a well-ventilated space or outdoors. If you’re sanding cured resin or working in a smaller room, wear a respirator with an organic vapor cartridge for liquid resin fumes, or an N95-rated mask for resin dust. Long sleeves prevent skin contact with drips you won’t notice until the itching starts.