Really, Matt's video sums this up but for anyone searching for the same answer in the future, the GlassCast 10 and 50 resins are extremely sensitive to low temperatures and if the resin gets much below 10’C (either in storage or transport), it can begin to crystallise, at first becoming milky and in extreme circumstances becoming quite hard with the process; this does not damage the resin at all and can be reversed by heating the resin in its container with the lid securely in place. However, if the resin is used when it is in this crystallised or semi crystallised state, it could result in potential curing issues.
To reverse the crystallisation, you’ll need to hold it at 40-50°C+ or indeed even hotter for a few hours as it does take a bit of energy to reverse the crystallisation. You could achieve this by standing the container in boiling hot water ensuring the cap is tightly sealed (although you would have to change the water a few times to maintain the temperature) but this will return the resin to its clear, liquid form ready to be used for your project and, when returned fully to clear, it will cure faultlessly.
We're actually putting together a video of our own to show this process as well.
If you have any issues at all, please don’t hesitate to get in touch.