Because some books said that metal is red hot when annealed many
people heat the metal until it glows red. Under contmeporary lighting
conditions this is very bad for your metal. In fact it seriously
damages the crystal structure of the metal if there is any further
extended deformation; drawing, rolling, chasing, raising, forging etc
going to happen to it. Overheating causes grain enlargement which may
eventually lead to cracking in the metal. This will not really matter
if the work is only being used for construction or is at the end of
its plastic working. The descriptions of glowing red come from the
days when there was no electric light and the soldering area was in
the darkest part of the shop and consisted of a forge. The actual
color is the red you see in Concord grapes, barely red at all. If you
see any visible red light coming off a piece of metal under normal
room conditions today it is already overheated. Therefore we need
other indicators for when the metal is annealed.
Temple sticks and crayons are waxy materials used by welders. If the
Temple stick melts you have hit a certain temperature. Messy to clean
Borax flux goes glassy but then you have to clean it off.
Blue carpenters chalk turns white.
Ivory soap turns black.
A bamboo skewer or piece of wood leaves a trace like drawn
A permanent marker will disappear.
My favorite method is to watch the flame color. It will turn
distinctly yellowish-orange the moment that the metal surface hits
about 800 degrees F. This is the temperature that carbon particles
glow incandescent and it means that unburned carbon particles in the
flame are hitting a surface with that temperature regardless of what
material that surface is made of. This is however below the 900
degrees F that is called ‘black body heat’ which is the temperature
that materials begin to give off visible light. In practice by the
time you have recognized the yellow flame and reacted to it the
temperature will have risen somewhat and you will be at about the
right temperature for all the metals that we are concerned with. (Yes
I know they all have different annealing temperatures but given the
need for average accuracy and speed of working this is a good
the above from the book "Cheap Thrills in the Tool Shop"
Box 1624, Ste M, Calgary, Alberta, T2P 2L7, Canada