Hello. I've tried various rust bluing formulas over the years and in the end, I've always been very happy with the results that I've gotten with the Mark Lee product.
I'm currently working on a Carcano project that someone gave me. I've done numerous cycles of rusting and boiling on the trigger guard, but the metal just doesn't seem to blacken.
I ordered new solution today. Just wondering if anybody has some input?

Sure sounds like incomoplete cleaning..Some of these new lubricants are pretty tenacious....and the agressive cleaners of the past have been found to kill horses and babies (well..you know what I mean)

Get your rust bluing solution from Bobster, here on AR. Yes, clean is non negotiable.
I use scotch brute pads and Tide; removes anything. I hope you didn't polish it with a buffing wheel...
Steam, no need to boil 8 gallons of water. Use one quart.
Bob will probably chime in now....

acetone?
simple green?
ultrasonic with simple green solution?
throw them in a NOT ALUMINUM pot and boil?

"Acid" test -- wipe some plumb brown on it and see if THAT bites?

Is the guard the only part you're having an issue?

I know nothing about Carcano's but could it be the metal itself?

I’ve had this issue also and not isolated to just Mark Lees. I talked to Mark on the phone and his advice made the most sense, although I have yet to blue anything and test the theory. All the normal answers were given by multiple people, cleanliness, water, blah blah. I covered all those bases over and over. I’ve done plenty of good blue with the same technique, water, solution etc. Mark suggested that the initial carding may not have been aggressive enough and in his experience can set up the problem of the gray tone vs black. Again I have yet to test the theory but I suspect there is something to it. I had been experimenting, rusting very lightly and carding quick and gently trying to achieve a finer grain/texture when I was fighting this problem.

Please report back if you find the problem

Mark Lee's #1 Express Blue is just that,,an Express Process.

Are you using it as such,,or are you using it as a Slow Rust Blue?

It won't work as a Slow Rust Blue soln.

It's meant to be applied to clean, WARM, steel parts.
It will turn to brown, rust color immedietely.
Then they go right into the boiling water tank (or into the steam tube if you are using that.

10 or 15 min,,pull them out. Shake the excess water off,,most will evaporate by itself.

Now card the pieces.\

If still hot enough, recoat with the soln and repeat.
If they have cooled off,,re-warm them with a propane torch or other heat source.
No need to heat them any hotter than around 200F.
The old method was to simply put them abck into the boiling water tank to reheat,,then pull them out and re-coat with soln. Then right back into the tank to turn brown to blue.

If you are doing all this already, my apologys.

It may be the metal isn't clean enough.
Sometimes, certain steel alloys just don't respond well to Express Blue formulas of certain chemical make up.
You have to try another or go to a Slow (cold) rust blue for those particular pieces.

When using any of the Rust Blue solns, pour out a small amy into another clean container to work from. Don't keep getting new soln right from the bottle that it came in. That's a sure way to contaminate the main bottle/source.
Any small amt of oil that drags off the gun surface onto the patch used to apply the soln and then back to the bottle for more will contaminate that whole bottle.

Work from the small source and then dispose of it when done. Or if you keep it, use it for quick and nasty small jobs like bluing screw heads and the like.

I doubt it's the issue here,,but parts that are case hardened will usually be difficult to Express Rust Blue. Often they will 'take' the Express blueing but that will easily rub right back off.
One trick to get those parts to Express blue was to etch the warm surfaces with weak acid soln (nitric usually) before the first coating.

Thanks for all of your responses. I have been very fastidious with cleaning the parts and wearing nitrile gloves. I have not had issues when I've used the same technique before.
I have a bottle of Laurel Mountain Forge browning solution that I've used on my flintlock build. I'm going to give it a try.

I'd recommend using a Rustblue formula. American or German would do a good job. Degrease well per above. Make sure water sheets to prove degrease has worked. Use a 1:1 muriatic: distilled water pre-pickle cold for about a minute. Rinse, dry and begin Rustblue process per directions. Two passes should do it.

Bob
www.rustblue.com

I was given a tip years ago...first coat with Mark Lees Brown, then finish up with express...I think the idea is the same as Bobster suggests with the acid bath...i.e. get a slight "bite" ..even a light bead blast works well

Do what Bobster said; I have used other brands of rust blue solutions; now I only use his.
And yes, the water test it paramount; if it rolls off, something is wrong. Then if it doesn't rust, it is stainless.
I only steam.

quote:

Originally posted by fjrdoc:
Thanks for all of your responses. I have been very fastidious with cleaning the parts and wearing nitrile gloves. I have not had issues when I've used the same technique before.
I have a bottle of Laurel Mountain Forge browning solution that I've used on my flintlock build. I'm going to give it a try.

Some of those 'rubber' or nitrile gloves have some sort of powder or something on them. Might be contaminating the surface of your parts. I wear those white, knit glove liners when express bluing or slow rust bluing. I wear those awkward big black rubber cloves with the extra long cuff when I hot blue.