Durcupan
Durcupan is a water-soluble epoxy resin produced by the Fluka subsidiary of Sigma-Aldrich. It is commonly used for embedding
electron microscope samples in plastic so they may be sectioned (sliced thin) with a microtome and then imaged. Durcupan is notable for refractive index nD20 of 1.654, which is a very high value for epoxy resins. References

Electron microscopy
Synthetic resins