Hobbyists commonly choose casting acrylic for duplicating model parts and modifying existing projects largely because it is widely available from most hobby stores. Sold as a kit, casting acrylic comes as two liquids, liquid acrylic and a catalyst that cure into a plastic resin when mixed together. Although the casting process is simple, problems can arise due to bubbles in the acrylic or improper measuring. You can minimise such imperfections by following to a few simple tips.
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Use Mold Release
Mold release is a liquid that you brush or spray onto your mould before casting your acrylic piece. It keeps the acrylic from sticking to the mould. The kind of mould release you need depends on what your mould is made of as well as the acrylic itself. If you can, purchase a mould release from the same company that makes your acrylic for maximised compatibility. If this is not possible, you can try homemade alternatives. For plaster, latex and silicone moulds, use liquid wax as a mould release. However, often you don't even need a release for a silicone mould. The only sure way to know is through making some test pieces.
Use Exact Measurements
Always follow the instructions that come with your acrylic kit when mixing the acrylic and catalyst together. Imperfect measurements can lead to poor results, such as a resin piece that never quite fully cures and feels sticky to the touch. Most kits use a one-to-one ratio of liquid acrylic to catalyst, but some use a different ratio. Double check to make sure you are measuring correctly, and use graduated cups to measure out precise amounts of each.
Use Talcum Powder
Most companies use vacuum chambers that provide uniform, bubble-free results for every copy. This is rarely an option for the home enthusiast and bubbles often form in home-cast acrylic. However, brushing the inside of your mould with talcum powder can help minimise bubbles as well as ensure that the acrylic gets into nooks and crannies that it might otherwise miss. However, do not use this method if you wish your cast piece to be transparent, as the talc may stick to your cast piece.
Warm the Mold
Warming your mould will also help to minimise any bubble formation in your acrylic. But do not heat your mould up too much. You want it to be warm but still cool enough to hold. Some mould materials react badly to being heated up too much and may break down.
Sand Your Casting
If your end result has seams or rough spots, you can often repair these imperfections by sanding them away. Try using a slightly rough piece of sandpaper at first, around 400 grit. Then switch to a very fine grit sandpaper, 600 or over, for a polished result. Wear a dust mask to keep from inhaling plastic particles.
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