How to see colors of heat.

[Glenn]

Everyone's eyes are a bit different in the way they see color. The age of the eye, health of the eye, glasses, tints in the glasses, life experiences etc, etc, etc. Then there is where you view the metal, in the open, the shade, the sun, inside, under what type artificial light, inside a box to shade the metal etc, etc, etc.

To try to standardize color I suggest the following:

Black - no color

Low red
Medium red
High red

Low orange
Medium orange
High orange

Low yellow
Medium yellow
High yellow

White
Starting to throw a spark or two
4th on July sparkler

------------------------------------

Machinery's Handbook 12th ed.

752*F red heat, visible in the dark,
885*F red heat, visible in the twilight
975*F red heat, visible in the daylight
1077*F red heat, visible in the sunlight
1292*F dark red
and 2912*F Dazzling white (blulish white)

From 975*F to 29012*F is a difference of 1937 degrees. By dividing that into 12 different categories, we have 161 degrees between colors. By using the color list above as a standard, we come close to the same heat temperature and can now communicate color. Yes, you see the difference between red and orange a little differently than someone else, but the 12 color division lessens that difference.

Another factor is the type of steel. If you both are talking about mild steel, the system works. If you talking about tool steel, the system works. As long as your talking about the same steel, the temperatures should be close when referred to by color.

If you know of a better way to relate color temperatures (without pyrometers or temporal sticks), please let us know.

[HWooldridge]

Glenn, that's a really good breakdown - I hope everyone digests it.

Part of it is what you get used to - I knew a farrier who could forge weld on a bright sunny day with no shade but those were the conditions he usually worked in so he got used to them.

I have to have shade of some sort to judge colors - sunny, clear day under a tree or awning is fine but I can't work without some sort of roof.

[Nick]

That's the very same scale I use, except that instead of "high" I use "bright."

[Mike Turner]

Glenn this is pretty cool, I know for me I tell forge welding color better outside in the sun because that is what I do for a living as a farrier, I found when I started welding inside I was wanting to pull the steel to soon as it was the color I was use to outside. Now when I feel it is ready I walk away and wait a few more minutes then it is just right.

[Glenn]

The scale will slide according to light conditions, but throwing a spark is still the upper limit before burning of mild steel whether it is inside or outside. It is the lower end of the scale that moves from 1077* to 752* or about 325*. This is about a 27* change when divided out across the entire scale.

Depending on your situation, changing viewing conditions can throw you off when seeing colors. If you use the suggested standard, you can figure that the 325* change (visible in sunlight to visible in dark) is about 2 levels of color (2 x 161*). If you then drop everything two levels, you are close to a conversion with the slack now at the top end. This means that what should be throwing sparks (dark viewing) is only medium yellow or high yellow (daylight viewing).

[ThomasPowers]

One problem with the "traditional Cherry Red" is that they were talking about pie cherries which are more of an orange to yellow colour (not the dyed things some folks find in cans) while most people today only know bing cherries or the dyed in cans pie cherries---a very different colour indeed!

The other problem is that a lot of the old books were for people working wrought iron where "lemon yellow" is a *good* colour to work at.

Thomas

[habu68]

Another Trick, I've heard of, was to take a 7 gallon steel bucket and cut half the lid off and mount it on its side on the end of the forge. You stick the piece into the dark container to check color. The darkness in can gives a "standard" light condition.

[ThomasPowers]

and in shadeless areas of America a barrel was used the same way during pioneer times.

[Dale Russell]

Colours ,
that's fine for you lot who can see em , me , i's " red / green " colour blind . I do see a " colour " i call red / green , but can't tell the diff between lite or dark until another " red / green " is put next ta it .
Took me awhile to figgure out ow ta tell the rite temp ta bring iron outta fire , burnt up a HEAP of iron till i did ( worked my arm/ shoulder ta death too poundin' cold iron as well )

Dale Russell

[Frosty]

While this might not work for our red/green and other color blind friends (please let us know if you try it) it should work for others.

There are lots of color charts in books and a number online. Take the book or print out to a paint store and ask for color chips. Paint stores routinely give away color chips. Match them to the heat colors on the chart, take them home and glue them in order to a stick, the leg of your forge, etc.

Match your steel to the chart till you develop an eye for heat.

Be aware the accuracy of printed charts will depend on how well your printer is calibrated. Finding a book with a current chart would be preferable.

Frosty

[evfreek]

It is hard to use the charts, since they subjectively assume how much ambient sunlight is mixed in. See, for example, the following links

http://www.tempil.com/PDF/Basic_Guide.pdf
die block, alloy steel bar, steel die block, exporters of die block, hot & cold work tool steel, forging die steel block
Using the Fire
Heat & Temperature
HEAT COLORS

The viratsteels link seems a little too white at the high end. The others look kind of dark at the low end. The blksmth link has colors that are inconsistent with the text descriptions. But it looks close in the 1900 F range.

I think that you have to calibrate your eyes. The tricks of melting aluminum and copper are well-known, and may be enough to do the job (unless color blind).

Here are some other links:
kiln cigarette orange cone
argentium permanent marker

These aren't really links, they are mnemonics which can be used as Yahoo search keys.



Edit: dead link removed

[teknition]

I know you said no "pyrometers" but would a non contact temp gun count as such? I kind of think of a pyrometr as a temp display with wires on it running to the forge. Over here Ive seen temp guns on sale for as little as 29.00, so in the US you could probably find the same thing for 15.00

I figure why worry about exacting color right away... get a temp gun, get the steel close to the color you think it should be then pull it out of the forge and shoot it with the temp gun... do that for a while and pretty soon youll be able to associate the color with the temp, and if not, you still have the temp gun to check it with.

[evfreek]

I know you said no "pyrometers" but would a non contact temp gun count as such? I kind of think of a pyrometr as a temp display with wires on it running to the forge. Over here Ive seen temp guns on sale for as little as 29.00, so in the US you could probably find the same thing for 15.00
...

The problem with the cheap temp guns (they are actually optical pyrometers;) ) is that they do not have an interesting range. For example, the one currently on sale in the Harbor Freight catalog limits out at 110C, hardly useful for even tempering. It is not worthwhile to try tricks like extending the range with a filter, since the detector's wavelength is too long, and since radiance at long wavelengths does not change as markedly as at shorter wavelengths, there will be an accuracy problem.

You can get optical pyrometers that go up pretty high, but they will be costly. It is also possible to build a disappearing filament pyrometer with a light bulb, but it will require calibration. The temperature will go approximately as the power input to the 1/4th power, so that can be used to interpolate the calibration. The eye is not very sensitive to differences in brightness above 1900F, so this method pretty much gives out and you have to do tricky things like using red filters.