It's kind of hard to tell if the spring on the upper lock is broken at the bend, but it does look odd. The color of the break is likely a result of being in the heated solution.

I think Dean is spot on..could also have had a nick or other imperfection as well as an improper temper/ht but ultrasonic sure does shake things up with very small and rapid motions...not always so good for a part with a lot of internal stress.

I had both springs break in a Simson (Merkel) from having been setting cocked for a long period of time and once I started using the gun as intended.

This is very interesting. Over the years I have ultrasonic cleaned LOTS of parts and never had a damaged barrel set, part or spring. I use diluted dollar store cleaner degreaser in a heated tank. Hard for me to believe ultrasonic cleaning that won't damage case color, solder joint or blueing and won't touch rust will damage sound spring steel. I have never used simple green.

When my main spring broke on the 1861 repro lock plate it had been in the Brownells Steel White overnight. It had not been touched. The solution and lock plate were both at the same temp. as they were both stored in my garage. No agitation. Just sitting in the solution. Pulled it out and the spring was broken in two pieces. Now this spring was probably only twenty years old.

Hi,
While the upper spring appears hopeless. I once repaired a break like that on the lower spring where the break is at the point where the spring turns a 180 deg corner. I stuck both ends into a potato to keep them cool and silver soldered the parts back together. The spring has worked fine for 40 years. I have also had good results making springs from the steel that you get from brownells. I have never tried to make that kind of spring however.
Regards
Preston Chaney

It is not generally known and/or accepted as possible, but flat springs like this can be welded... but not by just anyone. It takes an expert to do it right. The result is a very functional spring, if its properly cleaned up.

This is a perfect job for the experienced "micro welder."

It now appears that broken springs can be achieved without ultra sonic cleaners.

I recently soaked the assembled action and locks of an English sidelock in lacquer thinner for about 24 hours to clean them. Then allowed them to dry out in the sun. Then at some unannounced point, two springs simply BROKE !!! One the left lock's mainspring. The other, the safety roller spring. Both of which worked and appeared fine previously... only dirty.

I have never had this happen before. And can only think that the springs had failure points already, and the solvent allowed them to manifest the weakness.

No ultra sonic bath needed.

I guess you learn something every day...