METAL HEAT TREATMENT, carbon stopoff paste for carburizing
Out of curiosity I looked for this product you describe, and I can't find any manufacturers on the web nor can I find any reference to such a product. Does such a product really exist?....
Nonetheless, I did find this discussion on the metal finishing site which talked about trying to control inadvertent decarburization by using a copper plating. See http://www.finishing.com/0600-0799/619.html