Copper Electroformed Layer "Upset" by Extreme Heat

I am a graduate student working on a second master's degree in metalsmithing. I am writing my thesis and have a challenge that I have been unable to solve.

After copper electroforming small copper or sterling silver vessels, I subjected them to extreme heat with a natural gas/air torch. This "upset" the electroformed layer, leaving it cracked, buckled, split and separated from the core vessel in areas. It left the core vessel exposed through the splits. The solution I used was a little over a year old; I did not mix it and therefore do not know the exact recipe of this solution.

In January I mixed a new electroforming solution:

12 oz battery acid ⇦ on eBay or Amazon [affil link]
2 lbs copper sulphate
1 gallon distilled water

After electroforming more vessels, I subjected then to heat as before. However, regardless of the amount of heat I subjected them to, (almost melting the copper in areas) the electroformed layer would not react to the heat.

I want this "upset" layer and can not get these results again. I have tried to change every variable that comes to mind including different amps to length of time left in the bath ratio. I am convinced that 1) I need a different ratio in my solution recipe or 2)I need to leave the solution sitting for a year (would it chemically change?)

What would need to be changed in my recipe to get an electroformed layer that might react adversely to heat?

My thesis and exhibition is scheduled for July and I am needing to solve this challenge. Any help would be greatly appreciated.

Thank you,

Organic brighteners are co-deposited if they are in the solution, and they will cause brittleness and related problems at high temperature. My guess is that the old solution included organic brighteners.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey