I solder in an area that cannot be made dark enough to use changes in
the color of my metal as a temperature indicator. I can pretty
reliably use changes in the appearance of paste flux as a temperature
indicator instead; however, when I use a liquid flux like Batterns or
Pripp’s, I’m flying blind - I don’t know what changes to look for at
what temperature. Is it possible to explain what I should be seeing,
or is it a “you had to be there” kind of thing that should be seen to
Linds, I apologize that I do not have time to answer you question at
this time. Below is a small portion of Lesson 4 of my Online
Silversmithing class that may help you. I use Battern’s Self Pickling
Flux (I put it is to a spray bottle), and I only use hard solder for
every solder joint on every piece that I make. I only want you know
that because of the different melting temps of solder. I teach my
students that when they see the flux melt, to move their flames to
the solder joint and the solder will flow.
If you (or any one on Orchid) would be interested in more about how I
teach only using hard solder, and understanding more about this flux
question, email me and I will send you the first four lessons of the
Online Beginning Silver Class for free. Just email me and ask for the
"free four lessons". Please put “Free” in the “Subject” field.
Taken form Lesson 4
Flux goes through several stages as it does it job. We will spray it
on. We will use a $1.00 spray bottle from Wallmart or other such store.
So it goes on as a liquid and as you heat it it drys in to a crust.
This crust can be quite bubbly. As you keep heating the flux it will
smooth down to a thin coat. Then as it is heated to a higher
temperature it actually begins to melt into a syrupy brown fluid. It
is important for you to recognize each of these steps. As I solder, I
watch the flux as much or more than the color of the silver or the
solder, to determine how hot to get the piece for soldering. Just after
the flux melts in to small “puddles” of a brown “syrupy” consitancy
(you can take your “nudgit” and actually move this “syrupy” flux like
a thick liquid.), the solder will melt and flow. I believe that the
flux melts in to these puddles at about 100 degrees before the solder.
– Don Norris @Donald_Norris PO Box 2433 Estes Park, CO 80517
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