Forging fastener help

[Krups]

Hi there, I am trying to find the name of this product I used once to help me determine whether a forging die was expectable or not.
It's like putty but requires heat to mould it before it can be used to make an impression of something. I know its something obvious but just wondering what, where and which is the best one to buy. I'll probably purchase it out of my own pocket so price is important too.

Any help would be much appreciated thanks.