Artists rely on polyester and polyurethane resins when they need to do clay modelling and casting. These resins are ideal since they can cure and form a hard cast. They can also come off as glass, and shine through when they have been sanded and buffed. But one needs to choose which of these two to use. It is therefore important to find out more about their differences.
Polymer resins are not the most expensive options there are. It needs there to be a catalyst or an accelerator for it to work well. They on the other hand give off a toxic odor, which forces an artist to wear a protective gas mask as long as they are casting. There is also a need to work in a properly aerated studio. There must also be reinforcement in the form of a filler, like fiberglass. In future you can expect them to develop spider web-like cracks.
Polyester resins cure to a crystal clear finish, which is desirable. But they then turn yellow as they age after being exposed to UV light. They shall also be malleable for a short time, which needs the artist to work fast. They will be unusable after about ten minutes. They can be tricky to use due to their high and unpredictable shrinkage rate. IT makes for a good bond between fiberglass fabrics.
Polyurethane resins, on the other hand, are more costly. They however have more uses to them. They have found work in rubbers, plastics, inks, medicines, and more. They can take the abuse from chemicals, oils, grease, and abrasion better than others. They will also not emit the harmful toxic gases when casting.
They come in opaque and water clear resins. The costs they form will come with a lot of details and will not tear so easily. They also make for more choices, when you get the hardest as well as the softest plastics. They can easily form bubbles, which means you need to work on them in a pressure pot or vacuum chamber. You also need to have special colors to paint on them. This makes its choice of colors more limited than other options.
The only issue with polyurethane resin is the moisture sensitivity it has. You need to work on it in the right environment. If you work in a humid place, you need to invest in a dehumidifier. They also cure fast, which is ideal. You thus need to move fast in your working.
From this analysis, it is clear that polyurethane resins are the better choice for general mold making and casting works. They are thus preferred in a clay studio. Polyester on the other hand is best for fiberglass fabrications.