1967 Dime W/Unknown Image On Reverse, Help!

The area outside the hump-shaped line appears to be acid-etched. That's why there's a "step".

Someone else had suggested that as well. Is this an intentional process or just a fluke from an auto shop/industry? Thank you so much for your consideration.

Here is a 1979 dime I found lying around as a control to compare. Both the '79 and 67' are in similar condition. When you look at the control lettering around the perimeter it actually looks like the "image" on my 1967 is raised. Is it possible nothing has been removed =, only raised. the lower portion on my 67' looks to be at the right elevation in comparison to the control?

At first, I was hoping that there was an exotic die event explanation. It didn't look like typical forms of PMD. But after reading the thoughts of others and studying the pics more, I am in the old (literally, as in done a long time ago) acid etch camp right now.

1. It explains the "step" as Mike Diamond said.

2. It explains the different toning. The middle area appears brighter. The outside is dirtier and duller, especially around the letters. On the other hand, I don't see a way die events would explain the difference in toning.

An acid etch doesn't have to leave grotesque pitting or reduce the weight enough that the coin wouldn't still be in tolerance, even with a scale capable of enough precision to get an adequate measurement. In a previous life, I did these types of experiments on aluminum. With a mild etch, it sometimes was easy to see an effect under magnification that was almost impossible to get a corresponding mass loss on, even with balances capable of weighing down to the milligram level.

3. As another member said, the area around the E has a similar line which is bothersome to explain. Acid etch explains both areas. For the die event explanation to work, it would seem that two things would have to be going on at the same time.

Thanks to everyone! The amount of attention considering my find is flattering. I finally have a favorite web-site after all these years. You guys are great I've learned more in a few days than in the last couple years. I can't thank you all enough. I'll try to find something more traditional for my next post...?