Picture this. Those rings being brand new. Starting with the smallest diameter on the bottom. Getting progressively bigger in diameter until the top ring is bolted down. Each ring is held apart by small "bumps" evenly spaced around the bottom of each ring. The bumps hold the plates evenly spaced apart from each other. No where was there red brick looking stuff. Just good clean cast iron rings. Do yourself a favor and take the pot apart and reassemble the rings after they are sandblasted or wire brushed. Chances are there are one or more rings that are cracked and will cause a hot spot/ ring melt down. Easy / cheaper to change them as soon as they are found. Even if you have no cracked rings, your boiler will breath much better with a good ring cleaning. Sounds like someone tried to burn corn in it. It makes that reddish crap.