Glass to metal is pretty hard to do.
The reason that it cracked is because the glass and metal do not shrink at the same rate.
You need a really soft metal stretched out really thin so it can be crushed or pulled by the glass or a metal with the same COE as the glass you are melting.
You might try Dumet
http://www.teralab.co.uk/Glass_Blowi...eals_Page1.htm