Just finished a blue job with Mark Lee product and was very happy with my second rifle project. 3 weeks earlier I completed my fist rifle and had trouble with spots on the barrel. The only thing different was this time after degreasing I also wiped it down with Laquer thinner and then washed it in 409 and dried with paper towels. On the bad job used just degreaser and 409 and used clean cotton rags. Any suggestions ?

could be different steels. different alloys and hardnesses make different colors

Spots mean surface contamination. Do a better job of cleaning.
There is no advantage in using 409 after a good chemical solvent.
I like brake cleaner(aerosol) as the final rinse because it leaves no residue and will get the last few bits of oil.

RAN

I'm a big proponent of MARK LEE EXPRESS BLUE #1. It's what every other cold blue wishes it was.

I've never got a spot job on any of the numerous jobs I've done. I think the reason is, because I treat the metal just like I'm going to do a hot blue. I use Brownells and boil the metal with their cleaner in a SS tank. I boil in rain water between applications in rain water again in a ss tank. I again boil with the cleaner after the carding on each application.

No matter what blue you use, the metal has to be treated the same. Do you use clean cotton gloves for handling?

Never use any spray oils around your bluing area, no spray degreasers. You don't want anything in the work area that could contaminate the metal work surface.

Thank you, Use cotton - talked to Brnels - said do not put on too heavy - most spots are the result of drippey solution.