If scaling and decarb are your concern, a brush-on "anti-scale" compound is available from numerous places.

I use ATP641 anti-scale coating from Brownells.

It does a fantastic job of protecting the steel.

Brush on a light coat, soak in the oven at full heat - quench right out of the oven.

http://www.brownells.com/gunsmith-tools-supplies/metal-prep-coloring/heat-treating-accessories/anti-scale-coating-prod23076.aspx

I've used the ATP and thought it worked well enough. But, I've started using PBC Anti-scale and I like it a lot better. Bruce Bump told me about this stuff.

PBC is a dry powder. You heat the parts to 450 to 500 degrees and then either dip the parts in the PBC or sprinkle the powder on them. The PBC melts and covers the parts. A lot of the PBC will pop off during the quench. Any remaining PBC can be washed off with water. PBC does an amazing job of protecting the metal. I use it for heat treating gun lock parts.

PBC has been sold by Brownell's, but they don't currently have it. USA KnifeMakers supply has some listed.

PBC Anti-scale

Thanks so much guys for your speedy replies and the links. Anti-scale compound seems like it would be cheaper too.

Steve, why do you prefer the PBC to the ATP? It seems like it would be less convenient to apply, as the steel needs to be hot. Does it do a better/cleaner job?

Karl, is there a particular kind of brush that I should use to apply the ATP, or would any paint brush or rag do the trick?

Also, is one better for starters? I don't know which to get.

Jordan, I also use the PBC. Works great! I buy mine from Kayne and Son's Blacksmith Supply.

Bob

Steve, why do you prefer the PBC to the ATP?

The problems that I had with the ATP was some pitting of the steel. I believe the pitting was caused by the water in the mixture. I'll be the first to say that it could have been the way that I was using it. I tried letting the ATP dry overnight, drying it with a hot air gun and just putting it in the kin while still wet. All exhibited some amount of pitting. I didn't use the ATP long before I started using PBC.

My primary need for scale prevention is for heat treating parts for gun locks. I build all of the small intricate parts for a gun lock. The tumbler, sear, mainspring stirrup and bridle all have areas that are finished to the dimensions that they need to be when installed in the lock. Scaling and pitting in these areas would be catastrophic. I heard that Bruce Bump used PBC for heat treating gun lock parts for his cut-n-shoot pieces. I talked to Bruce and he told me the PBC was great. I got some and have been using it ever since.

To apply the PBC, the steel needs to be heated to 450 to 500 degrees. I usually just set my kiln to 500 degrees and heat the pieces with it. It really isn't a problem to use a propane torch or heat gun for the same purpose. With small parts, I just drop them in the container of PBC and sometimes use a spoon to pour PBC over them. For something as large as a knife blade, you will have to sprinkle the powder over the steel. I'm pretty sure that I often put more PBC on the parts than necessary, but it really isn't a problem. When you heat the parts to the temp for hardening, the excess PBC melts and runs off. Makes a little mess in the kiln, but not bad. The PBC melts and forms a paper thin coating on the steel. When you quench the steel, the PBC will almost all pop off. It's a little scary, as the PBC makes a crackling sound when it starts to break up. Some PBC will often remain in corners and tight areas after the quench. Hot water will soften the PBC and allow it to be scraped or wire brushed off. Just boiling the part in water works great and will remove all the PBC in a short time.

Another option to control scaling is to install argon injection on your kiln. Paragon sells an argon injection kit. I use argon injection for most of my knife blade heat treating. They provide instructions for the installation of the kit. It was pretty easy on my EvenHeat kiln. Argon is heavier than air. Your kiln should not be air tight, as the argon has to be able to push the air out of the kiln. But, the bottom half of the kiln needs to fairly air tight to contain the argon in the bottom. There is no way to predict the argon flow rate that you will need into your kiln, as every kiln and installation is different. You just have to play around with a piece of finished steel until you find a flow rate that protects the steel sufficiently. I have noticed that at the settings that I am currently using, the side the knife blade closest to the argon injection port is protected very well, but sometimes I get slight scaling on the opposite side of the blade. I could just turn up the flow rate. But, I feel that I could get good protection from the same amount of argon by installing a second injection port on the other side of the kiln. I'll get around to that some day…….

Paragon Argon Injection

I typically leave a carbon steel blade a little thicker and do heat treatment with out foil. You leave enough meat on the blade to grind off the heat treat scale. On a stainless blade, I typically go thinner, use foil, and plate quench with the packet on. With the exception of Steve's situation where dimensions are critical, I wouldn't use foil at all on a carbon steel blade.

Would a thin wash of satanite work?

Jordan, I use one of those disposable 79 cent brushes from the hardware store.

The blonde colored ones you can get in many different widths.

Although - I'm using the same brush I started using 2 years ago!

I haven't disposed of it.

I just let the compound dry and then brush it out later with a file card/brush.

I brush it on liberally and dry immediately with a propane torch.

Let it cool some and then apply a second coat if necessary.

Doing knives is not nearly as critical as Steve's gun parts.

We almost always regrind following heat treatment, anyway, to remove any possible decarb, so if there is any minimal pitting, it is removed anyway.

It's very simple.

Cal - above - said something about Satanite.

I find it pits the steel far too much. Protection from atmospheric conditions is not its purpose.

Since I regrind anyhow after heat treat, I do not use foil. Especially since I like hamons, just would not work. As for the thin wash of satanite, like Karl I found it will pit the blade being water based. Also with some steels even a thin wash can cause hardening issues. The only time I will use a thin wash is if I water quench which I do very seldom.

Brion

Thank you all so much for your helpful replies.

I think I will go with the ATP for now. It seems like it will be easier to apply and I don't really need to keep a perfect finish during the heat treat as I might with gun parts.

It's really cool to be able to get such great advice from so many amazing knifemakers.

Merry Christmas all.

Jordan