Resin

Casting resin is a synthetic liquid that is poured into a mold and hardens into a solid plastic. There are four main types of casting resin: epoxy, polyurethane, and polyester

Polyurethane: Polyurethane resins come in two liquid parts that once mixed, cure to a solid plastic. The curing process of polyurethane resin creates intense heat, so gloves should be worn and skin exposure should be avoided.

Epoxy: Epoxy resins come in two liquid parts that once mixed, cure to a solid plastic. In many cases, epoxy resin is more expensive than polyurethane and is often superior in strength. For some, repeated exposure to epoxy products can cause them to develop contact dermatitis, which is an allergic reaction of the skin. This can be easily avoided by wearing gloves.

UV Resin: UV resin is a one part resin that cures from exposure to the UV light. UV resin can only be cast in layers that have a maximum thickness of 3 to 4mm. Because of this, UV resin is more often used as a top coat rather than for casting. UV resins are also used in 3D printing where cured layers of resin are stacked on top of each other to create a 3 dimensional object. 3D resin printers are often used to create small detailed sculptures and jewelry.

Polyester:

General resin safety practices:

Some resins contain VOCs (Volatile Organic Compounds) that are harmful to breath and require the user to wear a respirator. Whenever using a new resin, be sure to read the safety data sheet and follow the safety recommendations.

Air Bubbles:

The process of mixing resin produces air bubbles that many users consider undesirable. There are multiple methods of eliminating and reducing air bubbles:

  • Avoid over mixing the material. Only mix the resin until the two parts are a single consistent color.
  • Pour the resin from high above. The thinner the resin pour is, the more air is released. 
  • Tap the mold after pouring. Tapping the mold helps the air rise to the top of the mold. A vibration table can also be used.
  • The best way to eliminate bubbles in resin is to use a pressure pot. Pressurizing resin shrinks the air bubbles so they become invisible.