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Heat coloring or bluing questions
- Thread starter John L
- Start date
- Joined
- Jul 23, 1999
- Messages
- 1,409
Heat coloring is a very fragile finish. Often is will "rub off" with routine handling. All steels within a given "family" will exhibit similar colors at given temps (carbon/alloy steels are what I'm calling one "family" and stainless would be another). Hues and brightness of the colors is dependent on on the finish applied to the steel prior to heat coloring.
The variety of colors will be the same as those achievable when tempering...from light straw, through slate gray. The limiting factor with most steels is that IF you exceed the tempering temperature of the given steel, you will destroy the heat treat....essentially creating something that has little or no use as a knife.
As with most things in knifemaking, it's a "give and take" situation....you give up one thing to acquire something else...in this case you will generally give up usability and finish durability in order to achieve "eye candy".
I'm not saying that is a bad thing, but YOU must make the choice(s), and be prepared to live with whatever, if any consequences result.
The variety of colors will be the same as those achievable when tempering...from light straw, through slate gray. The limiting factor with most steels is that IF you exceed the tempering temperature of the given steel, you will destroy the heat treat....essentially creating something that has little or no use as a knife.
As with most things in knifemaking, it's a "give and take" situation....you give up one thing to acquire something else...in this case you will generally give up usability and finish durability in order to achieve "eye candy".
I'm not saying that is a bad thing, but YOU must make the choice(s), and be prepared to live with whatever, if any consequences result.
- Joined
- Sep 9, 2003
- Messages
- 2,361
Your richest colors will be from 440F to 575F, the longer the heat the richer and thicker the oxide, but only to a certain point. Since it is the iron you are trying to oxidize, steels will less alloying will respond better in regards to nickel and chrome. I strongly encourage all makers to do some heat/fire bluing at least once to get a very sobering education about how reliable “colors” really are in judging tempering temperature. You will find how much those colors can be affected by a plethora of things other than temperature.
Surface prep is everything to the outcome. Satin finishes, due to the surface area and facets, will take a quick color with a different look than others. Mirror polish will be the most stunning in color and look but will be VERY delicate, the slightest touch can scratch it and will show like a black eye on the surface, and the only way to truly fix it is to refinish and reblue the entire piece. The most durable finish I have found is to bead blast and then blue, this will be a more subtle dull coloration that more resembles antique gun finishes, such as colored carburizing or Parkerizing, very similar to Parkerizing but with more color. The light will give slight iridescence from the many facets on the surface and any wear will be on the high spots, leaving more color and making the scuff less noticeable.
No oils at all on the surface! Do the final finish with gloved hands and don’t touch it again until you are entirely done. The heat needs to be extremely even and oxygen rich. For small parts you can set them on a metal plate and gently heat from below until you get the color you want, always stop a little short because the oxides will continue to form and deepen even after you remove the heat. For larger parts (I do entire rapier hilts) suspend the part in a large kiln and bump the temperature up incrementally to where you want it. Take the part out and allow it to set in the open air periodically so that fresh oxygen can do its job. There are no set temperatures for the exact color you want, every steel, every part and every day is different and I have never gotten the exact same color and effect twice, so it is best to do all of the fitting for one knife at the same time. You will be fascinated by how after 2 hours you can pull a straw colored piece of steel out of the kiln and turn around 10 minutes later to see it all purple.
Once the oxygen has had its way, and I have the color I like, I spray it down with a light oil (Wd-40 or other spray lubricants) while it is still hot until it is cool. This will change your color once again but will also add a protective element to the surface and set things. An odd thing I have found with the bead blasting method is that paste waxes will change the colors in an entirely different direction than an oil will and you could end up with a totally different hue than you started with, and it seems to be rather irreversible once applied.
All that being said the protective effects of heat bluing are surprisingly good. I have had mirror polished pieces that didn’t work out set in the corner for years and develop a good coating of rust in any places not blued but the blued areas only has a couple of specs here and there.
Surface prep is everything to the outcome. Satin finishes, due to the surface area and facets, will take a quick color with a different look than others. Mirror polish will be the most stunning in color and look but will be VERY delicate, the slightest touch can scratch it and will show like a black eye on the surface, and the only way to truly fix it is to refinish and reblue the entire piece. The most durable finish I have found is to bead blast and then blue, this will be a more subtle dull coloration that more resembles antique gun finishes, such as colored carburizing or Parkerizing, very similar to Parkerizing but with more color. The light will give slight iridescence from the many facets on the surface and any wear will be on the high spots, leaving more color and making the scuff less noticeable.
No oils at all on the surface! Do the final finish with gloved hands and don’t touch it again until you are entirely done. The heat needs to be extremely even and oxygen rich. For small parts you can set them on a metal plate and gently heat from below until you get the color you want, always stop a little short because the oxides will continue to form and deepen even after you remove the heat. For larger parts (I do entire rapier hilts) suspend the part in a large kiln and bump the temperature up incrementally to where you want it. Take the part out and allow it to set in the open air periodically so that fresh oxygen can do its job. There are no set temperatures for the exact color you want, every steel, every part and every day is different and I have never gotten the exact same color and effect twice, so it is best to do all of the fitting for one knife at the same time. You will be fascinated by how after 2 hours you can pull a straw colored piece of steel out of the kiln and turn around 10 minutes later to see it all purple.
Once the oxygen has had its way, and I have the color I like, I spray it down with a light oil (Wd-40 or other spray lubricants) while it is still hot until it is cool. This will change your color once again but will also add a protective element to the surface and set things. An odd thing I have found with the bead blasting method is that paste waxes will change the colors in an entirely different direction than an oil will and you could end up with a totally different hue than you started with, and it seems to be rather irreversible once applied.
All that being said the protective effects of heat bluing are surprisingly good. I have had mirror polished pieces that didn’t work out set in the corner for years and develop a good coating of rust in any places not blued but the blued areas only has a couple of specs here and there.
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