After letting the blade rest over night, we will begin to grind our bevels on the blade. The bevels are the angles that come down from the spine to the edge, that gives the knife its wedged shape. This is a repetitive job that takes quite a bit of time. I start with a 36 grit belt on my 2”x72” grinder. This is a special knife making machine and has the ability to grind at various speeds. Generally the coarser the belt the faster the speed, slowing down as you progress up through the finer grits.
Photo 1: Here I’m checking the grinding of the bevels on this blade and the thickness of the edge. Although I’ve already forged in the bevels there is a lot of cleaning up to to do by grinding. I grind here with the edge up trying to center my grind as much as possible. As I progress through the grits, I am also moving the bevels further up to the spine. A Gordo has what is known as a full flat grind, meaning that it is one straight angle from the spine at the top of the blade down to the secondary bevel which forms the edge. It is important not to grind too far up towards the spine and grind into it causing what is known as a broken shoulder. We want to take our blade to about 90 percent of finished. The edge should be just under the thickness of a dime. If we go much thinner at this stage we run the risk of the “deadly ping”. Too thin and a blade can crack during the quenching of the heat treatment process. When a blade cracks like this it makes a loud pinging noise, you’ll know it. I once ground a batch of my Horseman knives too thin and cracked 8 out of 10 of them during quenching. Man, I was throwing things around the shop and saying bad words and everything. You can bet I don’t go much thinner than a dime now. In this pic the edge is just about right. I proceed from a 36 grit belt, to a 60 grit, then a 120, a 220 and finally a 400 grit belt. It is important at this stage to refine the grind and get out any deep scratches or little ridges in the steel. These too can be a cause of the “deadly ping”.
Photo 2: Now we are going to anneal the blade. Like normalization, annealing is a time consuming step that many people just skip, period. This may sound funny but in order to get the most out of our heat treating process, which is hardening the steel, our blade must be as soft as possible before we heat treat. All the grinding that we have been doing and to some extent our normalization process has helped harden the steel. Grinding can create a lot of heat and to hold onto that piece of hot steel, I’m constantly dunking it in cool water throughout the grinding process. This can cause what is know as work hardening in the steel. What annealing does is get the steel dead soft again. So back into the forge goes our Gordo. We heat it up to about 1550 degrees (about a hundred degrees past non magnetic) and we let it cool very slowly. How we accomplish this is that I will take the red hot blade out of the forge and stick it into a can full of Vermiculite. Vermiculite is an additive that gardeners often use in making up potting soil. It attracts and holds moisture. Here we are using it as an insulation. I stick the blade in the can of Vermiculite and close the lid. I anneal first thing in the morning and the blade will stay in the can for 24 hours, cooling down very slowly. The next morning when I dig the knife out of the can it is cool to the touch and dead soft, ready to be heat treated.
Photo 3: Quenching in the heat treating process. Heat treating is the soul of any knife. It is the most important step in knife making. This is what makes or breaks a knife, (sometimes literally, remember our deadly ping). You can take a poor piece of junky steel and heat treat it well and produce a great knife. You can also take the best piece of steel on the planet and make a poor knife by heat treating it badly. Heat treating can be a relatively simple or very complex process depending on the steel. I can heat treat high carbon damascus, such as this Gordo or knives I make out of 1084. Other steels require more precise temperature control, for specific periods of time than can be accomplished in a forge. My blades made out of 440C or D2 come pre heat treated. They make fantastic knives, I just didn’t do the heat treat because its not something I can do in the home shop. In fact, stainless knives had and to some extent still suffer from a bad reputation as being cheap. It wasn’t that the steel was bad it was the heat treat process that was necessary to make a good knife from some stainless steels wasn’t understood yet. You can still buy a junky stainless knife, you can also buy a very high quality stainless blade. So how do I heat treat? The blade goes back into the forge. I want it to reach 1450 degrees and sit there for a moment or two. I then immediately quench it. The reason this photo is kind of blurry is that I am vigorously agitating the the blade in the quenchant. There will be a lot of hissing, popping, bubbling and smoke but hopefully no pinging! I use a commercial quenchant that has been engineered for this job. It has also been preheated to about 120 to 140 degrees. I will keep agitating the blade in the quenchant until I can touch it comfortably with a finger. Then I file test it to make sure the blade hardened. I use a triangular file, putting one edge of the file on the blade I try to cut into the knife. If the file “skates” across the blade we were successful. If it “bites” into the steel we will heat treat again. After heat treat comes tempering. We literally bake the knife in the kitchen oven for two hours at 375 degrees. This takes the brittleness out of the hardened steel. Our blade is almost complete.
Photo 4: Ready to etch. Prior to etching we do that last 10 percent of grinding to really refine our blade. Starting at 120 grit and this time going to 800 grit. It is important to never let the steel get hot at this stage, we could pull the temper out of the blade if we do, so a couple of passes on the grinder and dunk in water. This photo shows our Gordo at this stage of the process. All grinding up to 800 grit has been completed. Here I am cleaning the blade with acetone prior to etching. Damascus steel is several different steels forged together in layers. This bar of steel is then cut and stacked and forged together again. This process is repeated until the desired number of layers is achieved. There is an old wives tale that the more layers the better, that 2500 layers is better than 200. This simply is not so. It is the heat treat, the heat treat and the heat treat, did I mention the heat treat that makes a great knife. The particular damascus used in this Gordo is 416 layer. As you can see the pattern is not very evident. It’s there because the pattern is in the steel, not applied to the steel as many believe. The etching just brings out the pattern and a good etch should give us a little “topography” too, a slight difference that can be felt in the layers of the steel.
Photo 5: Dunking the blade. I’m sticking the blade into my etchant here. Many different things can be used to etch damascus. I use ferric chloride. It is a light weight acid I get at Radio Shack (used for cleaning circuit boards). I dilute it 4 parts water to 1 part ferric chloride and keep it in this old plastic coffee can. I will place the blade in the can and leave it there for about 15 minutes. I usually will do 4 or 5 blades at one time.
Photo 6: Here are our blades out of the etchant. Our Gordo is second from the bottom. You can clearly see the effect that the etchant has on the damascus and on these blades and how much of the blade was in the etchant. I don’t etch the entire handle area of the tang because its gonna be under the handle and not visible anyway. The etchant is then rinsed off in hot water.
Photo 7: Using 2000 grit wet or dry sandpaper, I lightly sand the blade where it has been etched. This brings out the highlights and removes some of the excess oxides which is the “black”. After sanding I will wipe the blade down with acetone to clean it up further and remove any loose oxides. It is then ready for re etching.
Photo 8: Our Gordo heading in for another etch. I sometimes do this 2 or 3 times. Just kind of depends on the damascus and the look I’m going for with a particular knife. This Gordo was etched 3 times giving high contrast and some topography.
Photo 9: The final step in our etching process. The acid must be neutralized so that it does not continue to eat on our steel. I make up a solution of baking soda and water. The blades are given another 15 minute soak in this base solution to neutralize the acid. Then they are dried and oiled to prevent rust. The oiling helps to fix and protect the oxides too.
We shall continue on shortly with building our Gordo by attaching the bolster and handles and shaping these into our finished knife.