Great
This stuff works great. I applied it and waited a few minutes. Using 000 steel wool the factory blue came right off. I used the 1:1 mix.
A must have in the shop
This is a great product for the easy removal of ALL rust including fine bluing and browning. Leaves a sticky residue on parts (hands and work area as well) that protects against flash rust so you can take a break or even overnight (comes off without effort using TCE, MEK or water). Parts left in a container of the solution will darken, most noticable if all of the part isn't complete covered. It is slow to remove bluing so you can remove rust spots with confidence and touch up with a quick bluing product.
Not Effective on Parkerizing
Took 2 soakings along with stainless steel brush scrubbing to get a Browning Hi Power slide and frame clean on the exterior surfaces. This was after removing the epoxy finish with paint stripper and a grinder wire wheel. It did finally get the exterior clean but all the internal parkerized surfaces were left untouched. I mixed at 3 parts acid to 1 part water. I suspect it would be more effective on traditional gun bluing but didn't help me much on this job. The results weighed against the substantial price not worth it in my opinion unless it's being used on a blued gun and it remains reusable for several jobs.