This stuff works pretty quick. I followed the instructions to the letter. Results are good, but not perfect - and it's all my fault. The product seems to work great. https://www.rustblue.com/shop/bluing...blue-american/
Here are some pics of my first attempt.
Attachment 118463Attachment 118464Attachment 118465Attachment 118466
pics are prepped part, parts after first rust, after first boil and carding, and after second rust + boil + carding. Final finish is actually darker than it looks in the camera lighting

The instructions call for a first application, parts at room temp, and let completely dry for 2 hours. Then, another coat, heat parts above 100F, then let rust.

The mottles showed up after that first prep coat, and became more defined in the first rusting.
After a second rusting, they went away but the edges of where they were don't. In short, I think the activation coat and first coat were were too heavy, and fumbling the parts around in my gloved hands didn't help as my fingers got wet with the solution.

After applying the solution, I heated the parts with a heat gun, put towel soaked with hot water in the bottom of my pot, and put the parts on top of a plastic lid. Sure enough, in an hour they were fine velvety red as in the pic.

I think the trick is to make sure the solution dries quickly before leaving in humid environment to rust. So, I lightly sanded just the buttplate to start over and try again, this time using my case dryer at 122F to dry the first "activator" coat, and heat the parts before the first main coat goes on.

Then again, looking over my original krag, which still has 75% or so of its original finish...there is some similar mottling on the loading gate and side plate. Maybe it has to do with the way they were case hardened?