I am tempering my 1095 blade at 425 deg in a gas oven with 2 thermometers to verify temp. Towards the tip, the color is purple, the rest, straw. The blade is on an aluminum baking sheet that is warped where the tip of the knife and the end of the handle is in contact with the baking sheet. Why the purple hue on the tip? According to charts, the tip tempered to 520 deg RC 58-59. Could this be correct? If so, should I re-quench the blade? The knife is more of a chopper 17" oal, blade 11".
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? color with tempering
- Thread starter radnur22
- Start date
daizee
Knifemaker / Craftsman / Service Provider
- Joined
- Dec 30, 2009
- Messages
- 11,176
If the color is a true indication of temper, your tip will be a little tougher, but less hard, than the rest of the blade. this might actually be desireable in a chopper.
I'm not sure what oven setting you used, but direct heat can overheat the blade even though the overall oven temp is at your target. You might try some foil over top of the knife.
My experience is also that colors are cumulative, and the tip would have spent more time at temp than the rest of the blade since it would come up to temp a bit faster. I'm not convinced that the color corresponds directly to hardness in this case, and that color as an indicator is more useful for a torch or forge temper.
I'm sure you'll get a more knowledgeable reply from one of the regulars soon enough.
-Daizee
I'm not sure what oven setting you used, but direct heat can overheat the blade even though the overall oven temp is at your target. You might try some foil over top of the knife.
My experience is also that colors are cumulative, and the tip would have spent more time at temp than the rest of the blade since it would come up to temp a bit faster. I'm not convinced that the color corresponds directly to hardness in this case, and that color as an indicator is more useful for a torch or forge temper.
I'm sure you'll get a more knowledgeable reply from one of the regulars soon enough.
-Daizee
SBuzek
Basic Member
- Joined
- Dec 7, 2006
- Messages
- 3,609
The color chart works with a clean blade and heating with a flame or touch.Tempering in an oven for the two hour cycle will give you all kind of colors from various contaminates.As long as you verify time and temp. you should be fine.
Not long ago a member here went throught the smae thing,his whole blade turned purple,he sent it to me,I Rockwall tested it and it came out at Rc60,
Stan
Not long ago a member here went throught the smae thing,his whole blade turned purple,he sent it to me,I Rockwall tested it and it came out at Rc60,
Stan