This balance is from a 17J 12s Illinois DR movement. S/N: 341080

Can you spot the problem?

I put the heavy side down in both photos....

Laid the balance side by side with a known good balance from a similar movment...

Silver speed screws threw me off for a minute. I was concerned someone might have harvested the gold.

One half of the wheel rim is bent outward too far?

The curve on the arm is something I will have to address, but is only a minor contributor.

This thing immediately goes to the heavy side.

Difference in weight between a gold screw on the heavy side and a brass screw on the light side???Also, gold screw looks like a domed screw v. brass screws are flat..

It's pretty amazing how much difference in weight there is between a gold screw and a brass screw that for all intents and purposes are the same size.

It was so far out of poise, I just sat and stared at if for a couple minutes, counting the weights, checking their locations, comparing to a known good balance in another watch...

And then it jut jumped out at me that the one balance weight was a gold weight. The gold screw is rose gold in color and lacks the patina of the brass weights.

Swapped in a pair of weights from a donor watch and she came right back to normal.

I did some digging.

Atomic weights:

yellow brass 192.5 ;roughly 1part zinc 2parts copper / varies with alloy
platinum 195 sometimes used for meantime screws
gold 197
lead 207

some gold screws are very soft and easily scarred , this I think would indicate a high karat.