Furnace Temperature Colors

goldsilverpro · Nov 5, 2007

APPROXIMATE FURNACE TEMPERATURE COLORS

Lowest red visible in the dark.......... 470 C ..... 878 F
Dark red, blood-red....................... 550 C ..... 1022 F
Dark cherry.................................. 625 C ..... 1127 F
Cherry-red, full cherry................... 700 C ..... 1292 F
Light red....................................... 850 C ..... 1530 F
Orange......................................... 900 C ..... 1652 F
Light orange.................................. 950 C ..... 1742 F
Yellow........................................... 1000 C ... 1832 F
Light yellow................................... 1050 C ... 1922 F
White.................................... 1150-1200 C ... 2102-2192 F

Noxx · Nov 5, 2007

Interesting thanks. But I taught that white was 1200C up to evaporation lol.

goldsilverpro · Nov 5, 2007

I think those numbers are when it first turns white.

mwren · Nov 8, 2007

Are these temps for flames inside the furnaces or for the flames that shoot out of the top?

goldsilverpro · Nov 9, 2007

I took them out of an old fire assay book. I'm sure they apply to the chamber of the furnace and the refractory although they could apply to any heated object - the tip of a cigarette, e.g. I would doubt if the flame colors would be reliable, since various flame compositions produce different colors.

Naitsabes · Nov 11, 2007

With all due respect a Slight clarification.

Every temperature has a particular spectrum so yes the numbers are reliable.

Color blindness excepted.

Unless of course there is a dopant that oxidizes and gives off a particular color as in pyrotechnics. Things burn in different colors according to their composition.

But everything material "glows" at a particular "color" related to its temperature be it one degree K or 1,000,000K

FrugalRefiner · May 17, 2015

Judging temperature by color is very subjective. The colors we perceive are affected by the surrounding lighting conditions. The first visible redness can be seen at lower temperatures in the dark than in sunlight, as shown on the chart.

I believe our perceptions are also affected by our personal experiences. If the brightest glow you've ever seen is red hot, it's hard to judge the shades of oranges, yellows, and whites. If you've seen the flash of an arc welder, you know what dazzling white means.

I combined the information from about a dozen different sources to create my chart, so most of the ranges overlap due to different terminology and temperatures among the sources.

I included the melting points of a few metals of interest.

The colors you see on your computer screen or those produced by your printer may be different than mine. I provide no warranty as to its accuracy. I've included a pdf file for those who would like a printed copy.

Dave

View attachment Heat Colors.pdf

kurtak · May 17, 2015

Very nice - thanks for doing this Dave - its another good one to hang on the lab wall along with the reactivity chart

Iron is up there with palladium

Kurt

goldsilverpro · May 17, 2015

Here's another chart that used to be hanging in almost every lab. It's an Excel file though. I don't know how they got a valence of +4 for gold, though. Last time I looked it was +1 or +3 or, rarely, +2.
http://chemistry.about.com/library/weekly/aa122002a.htm

kurtak · May 18, 2015

Thanks Chris - I just printed the Excel chart to hang on the wall

Kurt

72chevel · Jun 3, 2015

I have been melting anything I can, to get familiar with my speedy melt I purchased. I first started with aluminum that went well found its best to crush the cans first so they are not trying fly out before they hit the bottom of the crucible. I tried some copper wire I got out of motors this weekend and it did not go as planned. I threw about a dozen of those copper centers you find from cpu heatsinks and I am thinking now they were not solid copper. The speedy melt was up there in the white heat range but when I went to poor half of it stayed in the crucible and half came out into my cast iron pan but it got hard as it poured so it left a trail from the crucible to the pan! Kind of a mess!

nickton · Jul 14, 2018

When it heats to yellow it must be harder to distinguish the gold from the crucible color.

anachronism · Jul 14, 2018

nickton said:
When it heats to yellow it must be harder to distinguish the gold from the crucible color.

Not particularly.

g_axelsson · Jul 14, 2018

That looks solid, this is how it looks when melted. And I agree, no problem to discern the gold from the crucible.

Göran

glorycloud · Jul 14, 2018

Show offS!! :lol: :lol:

Love the sight of molten Au!! :G 8)

anachronism · Jul 14, 2018

g_axelsson said:
That looks solid, this is how it looks when melted. And I agree, no problem to discern the gold from the crucible.

Göran

Yeah you showoff I bet your blob wasn't 220g though was it ?

haha

g_axelsson · Jul 15, 2018

No, less than a quarter of it. Only 53 grams.

Göran

nickton · Jul 18, 2018

Maybe some day....

TreySeaJax · Jul 29, 2018

Dave,

I am new to the group. Really like that you posted this. Realized the practically watching gold melt. On the downside, what I think is about 12k gold probably has nickle in it.

Thank you,
Trey

Furnace Temperature Colors

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