Temper and Reharden Steel
When you are finished working the tool & have it the shape that you want it, you can re-harden & temper it.
Heat it red hot for an inch, or two back from the tip with the torch, then quench the tip in oil.
When the tip has cooled, remove the tool from the oil and quickly polish the cutting end with some emery cloth.
Watch the polished surface, as the heat from the opposite end feeds back into the quenched end.
As the temperature of the hardened end increases, oxide colors appear.
These oxide colors progress from pale yellow, to a straw color, and end in blue colors.
As soon as the correct shade of blue appears (this should be a peacock to purple), quench the entire tool to prevent further softening of the tip.
The metal is tempered as soon as the proper oxide color appears and quenching merely prevents further tempering by halting the process.
This final quench has no effect on the body of the tool, because the temperature will have dropped below the critical point by the time the proper oxide color appears on the tip.
When you have completed this process, the scraper will be
hardened and tempered and only needs a final grinding.
For more information, you can check out:
Machinery's Handbook, 26th Edition, 2000, Industrial Press
Edge of the Anvil, Jack Andrews, 1977, Skipjack Press.