HOT DIP CAUSTIC BLUING A KNIFE

published in Knives Australia Magazine 2007

The technique of bluing has been around for a long time. Riffle barrels and actions are often blued to minimise reflections and because its one of the very few techniques for colouring steel that doesn’t add dimension to the parts. I was interested in bluing my knife mainly for cosmetic reasons, though the process does bestow some resistive properties to carbon steel.

My initial DIY plan was to purchase a cold blueing solution from a gun shop and chance my arm with that. However the sales staff talked me out of this nonsense, confiding that the solutions wouldn’t give me the precise and even result a custom knife demanded. Nor would the finish be long lasting. Instead, they highly recommended a firearm restorer in the Adelaide Hills who specialised in hot-dip caustic bluing, commenting that he’d been servicing their gun clients for some time.

Darrol Haniford ( pictured at left, at his workbench) has been a firearms restorer for eleven years. Before that he had what many would consider one of the best jobs in the world, sales rep for a Beer company. His mechanical skills came from an earlier apprenticeship with Jaguar and tinkering with cars in general. Now-a-days, he happily acknowledges working in the shed has become a “full time hobby” but would stop short of calling it a business because he enjoys it too much.

Indeed, every time I’ve visited, his work bench is well spread with arms in different states of repair, from high end sporting guns to hexagonal section blunderbusses built like small cannons. He works up both the metal and wooden parts to a restorer’s spec and consequently suffers the artist’s pangs of loss every time he has to hand the unit back to the owner.

Up until recently he went hunting once a week. With age, this has crept out to every couple of months but he maintains many contacts through the field and helps his mob by making award trophies and those other decorative bits and pieces that allow  ceremonial nights and social clubs to function. In fact Darrol is one of those elder craftsmen who have a seemingly infinite list of names to draw on. His mental phone book of other artisans, each doing some prosaic and unique job is extensive.  Reaching for a faded and coffee stained hand written page on a clipboard Darrol says, “This bloke I know is coming over next week, he’s got a seven day long cool-bluing method developed by the Swiss Army” We both look at pages of process and I think it resembles a witches recipe more than anything scientific or industrial. Our conversation rambles and within a minute Darrol says, “And this bloke does colour case hardening, it’s taken him ten years of experimenting to developed a secret formula…. ”, and on it goes. It’s the kind of knowledge held by a village elder that should get passed down the line and not lost.

For all that, Darrol is new to bluing knives. Prior to meeting me he’d done four and therefore it was a bit of an experiment for both of us. At first we tried unsuccessfully to blue a D2 blade but couldn’t get it to take an even colour. On each attempt it seemed clouded by subtle patches of dark green or brown but my third attempt at an O1 blade came out like a beautiful black mirror.

The actual process starts at the knife makers bench-top. The final quality of the bluing depends upon the effort the maker puts into polishing the blade. If you are not prepared to put out for a mirror shine you will end up disappointed. Now that’s experience I gained the hard way. In my ignorance, I left the first 01 blade at 1200 grit, thinking the blueing process would bog up the scratches or the dark colour would mask them. The result was pretty ugly. In fact the bluing highlighted the 1200 grit scratches so much that the blade looked like it had been dragged down the lane under a truck.

Bear in mind that I’m specifically talking about a mirror effect because that’s what I like. I’m sure there are plenty of makers who want otherwise but for me the black reflections add not just class but something to aim for. I polished the 5160 blade made for this article to a healthy mirror reflection, as can be seen in the photo opposite.

If you want a matt finish you could consider wet bead blasting the blade prior to bluing, a technique often used by Darrol on his riffle parts. The end effect is quite sophisticated and I’m inclined to try this myself. Those wishing to blue carbon Damascus will have to find the level of finish they require as I haven’t been there yet.

Another point to bear in mind is that bluing is a surface coating distantly related to rust. It can be removed in the same way, therefore you need to get all the shaping, polishing and sizing up of the handle furniture completed prior to bluing. You do not want to be doing a lot of sanding on the spine of a full tang blade after the fact.

Which begs the question, how tuff is bluing? Darrel showed me some riffle barrels and bolts he was re-treating after 20 years of regular service and they still had most of their blue. The high-use areas that had worn were dark and shiny rather than the original blued-black and were well graduated into the better preserved darker surrounds. It’s not as if the bluing flakes off like cheap paint to reveal polished steel underneath. The colour is far stronger than that. More that it gradually wears to a lighter shade rather than the original black. Think of how lasting the treatment on a riffle barrel is, because it’s the same process.

Darryl kindly ran a test piece of 5160 with a batch of his other jobs prior to my making the knife blade. I didn’t want to find out the hard way that the finish wouldn’t take. I’ve since used this piece for unscientific and absolutely non-rigorous destructive testing of the finish. The results are best described as qualitative. A tungsten carbide scribe and hand files scratched the bluing while brass, nickel silver, mild steel and aluminium did not.

As I used pins to secure the handle scales, some final sanding to 2000 grit was required after the glue-up, though not on the metal. Polishing of the wood using an unstitched cloth wheel didn’t hurt the blued finish on the spine, nor did the final swans down buff.

Darrol says the biggest killer of a blued finish is salty fluid, including blood. If left wet or uncleaned for any length of time, a day or so, the finish will suffer. Rust pitting is not good. A blued blade with light surface rust can be restored by gently buffing with fine oil and super fine steel wool. Generally however, you would manage the maintenance of a blued knife in the same way as you would any other carbon steel blade.

Darrol assures me that the physical process of bluing is a stinking, caustic and awful thing to be party to. He was quite convincing on this point and I see no need for me to conduct my own experiments. There’s as much art as science involved. The job must be scrupulously cleaned of dirt, wax, grease, finger prints, etc in a boiling bath. The actual bluing and caustic bath which follows must be within a two degree range of just right, the immersion time must be judged on thickness and hardness of the steel. The job then has to be scrubbed of acid and allowed to relax for a day wearing a coat of fine machine oil. Essentially, it’s good to hand this over to someone who has the equipment and knows what they are doing. 

The processing tanks Darrol uses are 40yrs old and resemble fish and chip cookers, though festooned with coloured stalactites of chemical salts. The job is held within a mesh basket and dunked into each tank in turn. He does the work in batches as heating the tanks and slopping the chemicals is too lengthy a business and too much like hard work for one small part. I also get the impression that bluing is his least favourite part of restoring a firearm so he has to have good cause to suffer through it.

That being said, Darrol asked me to make it clear he would like to colour more knives as he enjoys the craftsmanship and wants to meet more makers. That’s totally understandable as there’s a lot of common ground. Both Darrol’s craft and knife making juxtapose wood or exotic materials against steel and strive to meld function, design and visual appeal. A similar aesthetic runs through both camps and the end products very much partner each other in the field. Interested knife makers are encouraged to contact him via the phone number at the end of this article.

So, to the example knife made for this story. I fashioned a camp blade from the 5160 bar using stock removal.  The blade was heat treated to RC58. It has a tapered tang, an upswept point strongly supported by a decent pyramid of metal and a deep belly. The handle is full palm length and simply clad in polished cocobolo with brick red liners. The overall appearance is dark with a highlighting flash of red.

Every time I come away from a chat with Darrol I’m burdened with ideas that I’ll have to try sooner or later. I suppose this means that all my knives will be one of a kind, because there are simply too many alternatives to explore.

Warrick Edmonds 20-8-07