Seve, I've noticed the same thing, but don't have an answer. I'm working on a knife, now, with damascus fittings. The are not hardened and etch differently than the blade.

Dale

Dale,

Most of us (at least I do) make our damascus knife fittings out of the same steels as we do our blades. When using ferric chloride to etch these steels, I see the non hardened damascus etch much slower and with less contrasting oxides formed. I have never seen an explanation of the chemical reaction that causes this. But maybe, we need to consider something other than ferric chloride and/or use different steels for damascus items that we do not want to heat treat.

My interest in etching non hardened damascus comes from my work with damascus gun barrels. I know that the damascus barrels made 100 to 150 years ago were not heat treated. Yet, were deeply etched, using sulfuric acid. I have talked to modern gunsmiths who are refinishing these old barrels and they are using copper sulfate to etch them. As I am now making damascus gun barrels, I am looking for an efficient method for etching them in the unhardened state. I do not need the barrels to be heat treated and do not want to subject them to the risks of a full hardening quench.

There is another world of craftsmen who etch metals to create artworks and printing plates. They use other variations of etchants for their work. None of their creations are in heat treated steel.

Maybe us knifemakers need to pull our heads out of the sand and look into what others are using to etch steel. Perhaps we can save ourselves some time and grief by simply changing the process that we use.

Mr. Steve,

I've been thinking about this since your first post. I'm not a metalurgist and I have not experimented other than I have etched edge-hardened and full hardened patternwelded blades and have seen what you observed so I hope this post doesn't come off as stupid. Could it be the carbon? I'm guessing the old damascus barrels are not high carbon like a blade. With martensite having carbon locked up with the iron and etching well while pearlite doesn't etch well and the carbon is free. I'm wondering if you could spheroidize or make bainite to lock up the carbon, and if you use salt tanks you shouldn't destroy any existing finish or subject your fittings to a harsh quench.

This was just a thought as I have sworn off damascus till I pass the JS test, so I will not be experimenting myself at this time. And if this was a stupid idea, just let me know and I will crawl back under my rock, although some days it feels more like a boulder!

Steve Seib

Hey Steve,

The things you mentioned are not stupid. At least I hope they're not, because they are exactly the things that I am wondering about.

As it has been seen that hardened steel etches differently than unhardened steel, at least with ferric chloride, it begs the question of what alloy phase or microstructure the steel should be in for efficient etching. But, do all chemicals suitable for etching damascus react differently to varied conditions of steel structure?

Our choices of etchants for steel are either acids, or metal salts (ferric chloride, copper sulfate, sodium bisulphate, etc.). I do not yet know how the chemical reaction differs between the use of an acid and the use of a metal salt to etch steel. I've been researching what people in other fields of work use for etching steel. Most of them do not consider ferric chloride to be a proper etchant for steel.

I haven't seen any explanation (that I can understand) of exactly what chemical reaction is happening between the steel and the etchant. A better understanding of this reaction may help with choosing the steels and etchant solutions that would give the desired results.

I also don't know exactly what the chemical make-up is of the black residue that forms on the steel during etching, giving us the contrast in our damascus. I've been calling it "oxides", but only because I don't know what else to call it. What the heck is that stuff??? An explanation of the chemical reaction should state what this material is.

Steve, you could be right about trying different etchants. I used wrought iron, for fittings, on a couple of knives. Etching in ferric didn't give me the effict I wanted. I finally etched them in hydrachloric acid. I got a good textured etch, but no color contrast. I cleaned them up and gave them another etch in ferric. Then I got the color I wanted. I haven't tried this with steel, I'm out of HCL, so I can't say what the outcome might be.

Dale

I forgot to mention in my last post some information on the old damascus gun barrels. As best as I can determine, they were welded up of laminations of wrought iron and mid to high carbon steel. What makes it difficult to learn what they were made of is that the barrel welders did not make the damascus themselves. After about 1830, barrel damascus was made in rolling mills. Huge billets weighing 150 to 200 pounds were welded between rollers and were then drawn out into rods for sale to barrel smiths. The barrel smiths simply went to the rolling mills and bought damascus rods in the patterns that they needed for the barrels that they were going to make. During the two world wars, the rolling mills were destroyed and all of their records were lost. So, there are no documents remaining telling exactly what the materials were that were used for damascus barrels. There could have been enough carbon content in these barrels to harden to some extent. But, I’ve seen no mention in writings contemporary to their manufacture of any heat treating process.

I am pretty certain that the barrel smiths did thermal cycle the barrel tubes after welding. I believe this because I have seen in written in several old publications of how the best barrels were cold hammered to “improve the density and tenacity of the metal”. Essentially the same as cold hammering a blade edge; the process effectively thermal cycling the steel.

The only etchant I have read being used on gun barrels was sulfuric acid. There were several finishes done on the barrels. Some were deep etched and left in the white. Some were black and white finish, like we do with many of our blades. Some were browned. Some were entirely blued to hide the fact that they were made of damascus.

The reason that I mentioned old damascus barrels was to point out that there are, and have been, other processes used to finish damascus items. And that some of these items did not undergo heat treating before etching.

Etching wrought iron is a crap shoot, I think. I have read a lot of old documents pertaining to the use of iron in the 19th century. Wrought iron was made to suit the needs of the end user. There was ship hull iron, boiler iron, anchor chain iron, structural iron, etc. The silica content was varied based on what the iron was going to be used for. So, different pieces of wrought iron may etch entirely differently, based on whatever silica content they contain.

I found this topic very interesting. Uneven etches at times bother me. I first noticed problems when I started using ferric and water, the hardened part doesn't etch at the same rate so it can look funny. But then I got to thinking when the blade is heat treated nicely the etch shows the skill of the smith. I used to use slfuric acid and water heated in a pyrex dish. It was rather dangerous but the results were great. I didn't have uneven etches that I can recall but this was in the late 80's early 90's and my heat treating skills were not refined to say the least. I was using mostly O-1 / mild/ A203E at the time. I learned how to use sulfuric from Bill Fiorini so what you said about gun barrels is especially fascinating. Bill also made damascus gun barrels and may be the reason why we used sulfuric. I do not remember if he heat treated them. I have some sulfuric (battery acid) kicking around in the shed. I may just go mix some up and do a comparison test on my next batch of blades! If nothing else I will have a great time remembering Bill. If you use the stuff please wear a respiator, chem gloves, goggles etc. -Hans Ruebel

Hans,

I had forgotten about this thread. I still haven't got around to experimenting with different etchants.

I talked to Bill Fiorini a few years ago, about his damascus barrel work. We never discussed etching. I doubt that he did any heat treating, other than thermal cycling to reduce grain size.

I do a deep etch in Ferric and after that a long etch in real strong Instant coffee for a black and white contrast. Maybe that works on unhardened damascus too, I never tried.