How do you color heat treated damascus?

[RDT]

How do you color heat treated damascus? Anyone have any tips? Thanks again....Rich

 

[indian george]

I hot blue my Damascus.

 

[rhrocker]

I.G., with a torch, oven, or salts???

 

[Arthur Washburn]

You have several options.

1st is standard bluing using a gunsmith. This is your best option if you do not want to affect the temper of the steel. I have a gunsmith that does my carbon/nickle damascus for 5 dollars a blade. I use this method on blades that may see use due to the fact that the salt bath is under 300f and will not affect the temper.

2nd and 3rd are nitre-blu and heat coloring. Both can and do affect the temper of the blade steel because the temps to obtain blues, purples and other colors are above normal tempering temps. I only use these methods if the blades are not going to see use. I perfer the Niter-blu method.

 

[fitzo]

I pass this on anecdotally to enable some discussion, as it has intruiged me since I heard it:

At the Chicago Custom show last September, I was talking about the nitre bluing of blades with a Montana bladesmith who makes marvelously complex mosaic folder blades that he nitre blues to get beautiful combinations of deep blues and reds. When I asked him about the loss of temper due to the high temp of nitre salts, his response was that he under-tempers by 25 degrees. His belief is that the subsequent brief exposure time in the bluing salts is so much less than a full temper that the hardness of the blade is not adversely affected.

I am not espousing this technique, having no data to back it up. Perhaps it would be worth discussing here....

 

[indian george]

I.G., with a torch, oven, or salts???

I use the low temp salts from Brownell.

 

[Laredo7mm]

How hot is the Nitre-Blu? One thing to remember about ruining the temper is that immersing the heat treated steel into hot liquid is easier to do than in an oven.

For exaple if the liquid bluing solution is 600 °F, and a tempering oven is at 600 °F, it will only take a short amount of time to ruin the temper in the liquid. Just because the transfer of heat is so much faster in liquid than in an oven. Conduction vs. convection. I know with my molten salts, it only takes a blade about 90 seconds to go from room temp to 1650 °F.

It would be nice to see some HRC testing done.

 

[fitzo]

The question though, is how quickly does the crystal structure change at a given temperature? A brief immersion at 600F would certainly not be the same as an hour at that temp.

And yes, I agree, Sean, some HRc would be in order. I've not got a salt pot.

 

[blgoode]

Good question Mike! I'd think that the blade is shot but what do I know?

 

[Laredo7mm]

Fitzo, that is one of the things I learned from Kevin Cashen at the Great Lakes Makers get together. I am paraphrasing, but it was something to the effect that; tempering martensite or the conversion from austenite to martensite is isothermal and instantanious and independant from time. Once the piece hits a certain temp the changes have happened.

So if you soak at 350 °F for two hours or 20, the results will be the same as long as the temp is the same. The whole reason for doing multiple tempers is to make sure you get the entire piece to the correct temp. Also the results are more reliable and consistant with multiple tempers.

Hopefully Kevin or Mete will see this thread and drop some insight on us. Because I could have mis understood.

 

[Kevin R. Cashen]

Fitzo, that is one of the things I learned from Kevin Cashen at the Great Lakes Makers get together. I am paraphrasing, but it was something to the effect that; tempering martensite or the conversion from austenite to martensite is isothermal and instantanious and independant from time. Once the piece hits a certain temp the changes have happened.

So if you soak at 350 °F for two hours or 20, the results will be the same as long as the temp is the same. The whole reason for doing multiple tempers is to make sure you get the entire piece to the correct temp. Also the results are more reliable and consistant with multiple tempers.

Hopefully Kevin or Mete will see this thread and drop some insight on us. Because I could have mis understood.

It was an odd chance that I did see this thread. Tempering is a diffusional process, so both time and temperature apply, although temperature is the most significant, but the temperature will require time to do its work. Exposure to a given temp will have limited effects fro short durations, but if one wants complete and even effects the time is necessarry for heat distributaion and complete diffusional processes.

The martensite transformation is "athermal" in that time has no relevence. When austenite reaches a certain temperature there will be instantaneous bursts of martensite lathe or plate formation. So converting austenite to martensite is strictly a matter of cooling. Tempering the martensite once it has formed is time and temperature. If one is converting more martensite from retained austenite with a secondary cooling (Cryo) the same applies; that is, if you convert a hypothetical 50% of a the retained austenite at a given sub zero temperature extending the soak is unlikely to convert more without further cooling.

If I miscommunicated on Saturday I must apologize, I was not firing on all my cylinders, in fact one should probably double check this post since my head still feels like it is going to explode at any minute.

 

[Laredo7mm]

See, told you I would get it wrong...

Thanks for jumping in and clarifying Kevin.

I was in a haze myself, but mine was from too many Jack and Cokes the night before....hehehe

 

[fitzo]

Kevin, if you see this again, would you offer your view on whether the temps/ residence time used for nitre bluing adversely affect the temper if kept to minimal timing? Could it be compensated for by undertempering a point or so RC? Thanks!