[TheForge] A different needle question

[Bruce .]

​I am altering the eye shape of a few commercial needles.  They're too
brittle to work without normalizing, but onc​
​e normalized, they bend just fine.

Now I need them hard again.  Well, dunking in water while at a red heat
works for that -- but leaves them more brittle than ever.

A tempering operation (to purple or blue, probably) is quite easy on a
chisel, but even SEEING the colors on a needle is a challenge.  For one
thing, there's no good surface to polish.

I've tried a couple methods, all without success -- my toaster over doesn't
get hot enough, like, maybe 450 F, despite what the dial says.   (520 F =
purple, 540 F = blue, 590 F = peacock, according to one reference.)  I
tried heating an iron griddle to these temperatures and leaving the needle
on it for about 5 minutes -- no luck.

I considered using a salt or solder bath, but find no appropriate salt and
that I'd need 80/20 to 85/15 lead/tin solder -- which is not readily
available -- to get a liquid bath of the right temperature.

I'm considering a sand bath or a furnace, using a thermocouple to monitor
temperature, but as you can see, this is getting increasingly complicated
for what should be a rather simple task.

Hence, I'm soliciting suggestions how to temper a needle.  Any notions?

Bruce
NJ