I have a practice plate with a Cerakote applicator now - he's giving it a test coat of a couple of the clear coats (air dry and heat dry).
He is as interested as I am to see what happens.
I should be able to report more in the next few days.
It may be good & id like to know the outcome of Gordon's test.
Being thinner than bluing may be a bit of a stretch since bluing is an oxide that forms in the surface of steel & not a coating like plating.
Using clear cerakote to protect something that has been french grayed would probably be fine. The big problem is that c-kote requires the surface of the metal to be balsted with 120 grit aluminum oxide to give it something to hold onto. It doesn't really bond with the surface of the metal and if handled much at all can start to flake off if not blasted and cleaned properly. If the applicator is not careful, it could very easily fill small details and once cured can only be removed by abrasive blasting. I am not a certified applicator but have been using it and have dealt with a lot o guns that have been coated improperly.
Weldon is correct as well. Bluing adds nothing to the dimensions of a part where any of the spray on / plated finishes do.
CeraKote will fill in what's left of the fine engraving details after it's been grit blasted.
Make them cuts deep and wide sans a lot of detail and you'll be ok.
I had an old Stevens shotgun to engrave (a sentimental job) that was going to be Cerakoted so I knew the cutting would need to be deep. It worked but the coating is not for "fine" work. The client was pleased but he spent way more than the gun was worth financially. It was his father's shotgun and he wanted it reworked for posterity. One day, when I figure out how to get the pictures off my phone I'll show just how rusted it was. It needed to be Cerakoted because the rust pits were way too deep to hide. I had to recut every single letter on it as they disappeared after filing and sanding. I personally don't recommend it.
I loaded the pics of the Cerakoted shotgun. Decide for yourself if the process is worth it.
A while ago I engraved and had a Colt 1911 CeraKoted and, I think, it turned out really nice. I have attached two photos of the gun to this post, but if anyone is interested in some higher resolution photos, they can be found on my website: http://lesengraving.com/colt_model_1911_1.html
Sorry it has taken so long to get back to you on my "test". My applicator lost his day job a couple days before he was to spray my practice plate and it put him into a tailspin of not having enough time to do my plate (???).
Anyway - I decided to give it a go myself. Cerakote recommends abrasive blasting to get a clean surface for the coating to stick to, or cleaning with a solvent - specifically tert-Butyl Acetate. I attempted to order some, however the hazardous material shipping costs preempted me from doing that (and not buying in 55 gal containers). The plate was not abrasive blasted and the metal above the antlers on the engraving was polished to about 2000 (the rest of the plate was finished to about 500 or less). It was cleaned several times with acetone, and the clear, air dry cerakote was applied. Apparently I still had some foreign matter in my airbrush, as there were some specks of finish that raised up a tad. The final look is that of orange peel - whether that is the cerakote or the applicators (my) fault - I'm not sure.
Cerakote recommends not touching the finish for an hour or so, and not serious handling for 24 hours, then 7 days before the finish is totally cured.
24 hours later is when the photo was taken (through the scope). The plate was taped off and finish was applied only to the right side. At this time, the finish chips easily.
I will continue to check it. I will also apply something to cause rust on the plate (rust bluing solution or muratic acid) in a few days to see how well the finish protects the steel.
No conclusions at this time, other than Cerakote may still be a possibility for a protective coating.
My applicator found a new place of employment (he is a timber framer) and got back on track with his second job (gunsmith). He had applied some heat cured matte and heat cured gloss clear to another practice plate I had provided him with. He also had problems with small specks in the spray in both the matte and gloss (as I had with air cure Cerakote). He had triple filtered both his solutions and both were only 1 month old (Cerakote has a shelf life of 1 year). He cleaned the plate with acetone and lint free cloths before applying the finish.
I measured the thickness of the applied finish - it varied from under .001 to .002 inch. Close to the specifications I have seen. It seems to "round-off" the details of engraving by drying thinner on the edges of the cuts. You may be able to see some of this in the photos - the shine near the cuts.
I ran a graver down some of the cuts - the finish peeled off very easily. Some chipping occurred along the cuts. The specks popped off very easily (on air and heat cured formulas) with an exacto blade.
Applying muratic acid caused the finish to be compromised - don't know if that is a legitimate test, but being told that it takes abrasive blasting to remove this finish causes me to wonder about the companies claims.
Both the applicator and myself agree that the clear Cerakote finish does not look good enough to put on an engraved firearm. This was certainly not a scientific test, however it has convinced me that Lacquer or Renaissance wax will be the way to protect a steel barrel on a stainless steel receiver.
Right side was taped off before applying Cerakote. Specks are visible at the top of photo. "rounding off" of engraving can be seen on left.
Cuts were chased with a graver and coating was easily removed and some chipping occurred on the lower cut.
I am not saying that clear coating with Cerakote will not work for an engraving - but it will not work for me! Note - this "test" has no results relating to colored Cerakote or Cerakote applied over abrasive blasted metal.
When you apply Cerakote you can wash it off before baking but not after it is baked. If you want to wast some money go ahead and apply it. You will be washing it off. I have some black I would gladly give to somebody. I did the tests and it looked terrible.