Shower – Weird brown line behind bathtub caulking

bathtubcaulkingshower

Earlier today, I found cracks in the caulking around my shower, so I removed the caulking to look for any mold or water damage. When I shone my iPhone light in that area, I found a weird brown line. (I tried scraping it away; it came off easily.) What is this line, and what may have caused it?

The first photo is a wide shot, to show what kind of shower I own. The second photo is a tighter shot of the area where I found the discoloration. The third photo is a close-up of the discoloration before I scraped it away.

Thank you for your time.

Wide shot of tub.
Region where I found the discoloration.
Close-up of discoloration.

Best Answer

Rust... you have a cast iron tub, the edges are which are up under the wall board and often exposed, so they rust a little and it runs down to the corner but stays there because of the caulk. Cast iron rusts a small amount, then the rust itself stops (or severely stalls) further rusting, I would not worry about it.