What colour is 'Cherry Red'?

I've just read in James Alford's thread on Brazing Brass mention of heating parts to 'Cherry Red'. It's a very common recommendation in technical books too. But what exactly is meant by it? Real cherries are mostly a dull red colour, but it's not uncommon to find them in much lighter shades. Cerise (which is French for Cherry) is a reddish pink whilst Glace Cherries are bright pink.

And under what lighting conditions is the colour to be judged? An active blacksmiths forge I visited was distinctly gloomy. My single garage sized workshop is far more brightly lit than the forge by six fluorescent tubes. It still isn't as well lit as my back garden at noon.

So what shade of red am I looking for, and am I looking for it in shady indoor conditions or in bright sunshine?

Thanks

Dave

Edited By SillyOldDuffer on 06/12/2017 19:23:45

You may well have answered your own question.

Found this list with some colours shown...

**LINK**

I did see on one site four different temperatures of "red" as in seen in the dark, twilight, daylight etc.

 

Edited By Brian Sweeting on 06/12/2017 19:40:07

Hi Dave

It's been a while since I done any heat treatment but what I remember is if you watch the colours changes,ie straw, blue the next should be dull red to 🍒 red.

I guess you will be queching, bending or case hardening, next will be molten metal ...hope this helps

Impossible to describe for all the reasons given. You could try heating a lump of steel up to 800C and see what it looks like under your conditions. A £15 multimeter from Chester () comes with a type K thermocouple that will indicate the temperature.

Rod

The original colours go back to(at least) the early industrial revolution and are an attempt to convert the temperatures which could not then be easily measured by the ordinary blacksmith into a system that could be demarked and seen as easily as possible. As such they are the colours of the English countryside. As time has passed there have been many attempts to enhance the system and now there are only the 'cherry' shades left of the natural adjectives that there once were. Also there are more shades now.

The 'cherry' shades (where still used) are; 'Dark cherry red, at just over 700 degrees C.....medium cherry red at just over 750 and 'full' cherry red at just over 800. The original colours were intended to be viewed in partial darkness away from the forge fire.

The basic 'cherry red' as originally used can be described as 'maroon' red, or dark wine red.

a word of caution;.....you need to practice a little at looking at the colours and it's not unknown for learning blacksmiths to mistake the lower colours at the end of the blue/purple/black red section at 400 to 470 with the cherry red area.

You need to turn your lights off as you cannot see the first red under electric light.

For brazing - in my experience the cherry red should be orangy red, not dark red, to get the filler rod to flow quickly, The quicker the metal is heated up the better as there is less chance of the flux deteriorating, so big nozzles are best. Prolonging the heating with small nozzles can lead to failure. and a complete cleanup and restart.

Similarly for hardening tool steel, dark red will not allow the necessary crystal change to take place and the steel will not harden when quenched.

For us not real cherry colour. Think of the bright red things mum used to get in a bottle to put on top of iced cakes as being full cherry red and work down.

In subdued light of course.

Stan Bray and others suggest boiled carrot as being a better approximation when hardening. Way out of date with modern supermarket tasteless carrot look alikes.

Clive.

Don't ask me! If you happen to be part colour blind, all options are possible! I could never see hot spots on a kiln shell, where the refractories had worn thin or dropped out, until it was veerry obvious to everyone on the shift.

'Sucking and seeing' with a piece of hardenable steel is the best way to go, I reckon.

If hardening, try the loss of magnetism trick and go for the lowest temperature that works satisfactorily, so scaling is minimised. Transfer experience to the brazing application.

It ought to be possible to actually measure the temperature using an IR/laser thermometer. Most of the common ones, admittedly, are barely up to this range but not so far out that one couldn't be made commercially.

Something like a Fluke 62 perhaps.

Edited By Bandersnatch on 06/12/2017 22:43:02

I am also colour blind (red and green) but I would describe cherry red as the point where the metal starts to 'glow' rather than being a flat colour. Obviously, this glow ranges from a dull red through cherry red to a very bright red - much further and you usually have a puddle with brass. I am able to detect this 'glow' at quite a wide range of light conditions but if I am right - cherry red is the really beautiful colour of the range.

I haven't done a huge amount of brazing (I've done more silver soldering at 600degC ish). I'd describe the brazing colour as more of a bright red colour.

Phil H

Cherry red is just above the point where mild steel becomes non-magnetic. Being blind in one eye and unable to see out of the other I tend to rely more on the magnet.

I 'red' an article that addressed this several years ago.

In the days when he description 'cherry red' was coined, the cherries most people knew were brighter red glace cherries rather than the drab things we find in the supermarket today.

My esteemed predecessor Stan Bray suggested that 'the colour of a boiled carrot' was more appropriate and that is what I go by.

Neil

I see Clive got there first!

Another thought, possibly because of the abundance of longer-wavelength IR, or because of an optical illusion, I always feel this is the temperature where the object goes into a kind of 'soft focus' but this may be because I wear glasses?

*reaches for laser thermometer on shelf*

Yes, boiled carrot colour works for me for hardening silver steel.

What is perhaps not always realised is that the colour is an exact measure of the temperature (see "black body radiation". What is imprecise is describing the colour and the effect of incident light.

Russell

Where did that **** smily come from?

Edited By Russell Eberhardt on 07/12/2017 09:21:48

The bracket that you originally had in before you edited it out! It's the alphabetical (symbol) code behind smilies.

To stop it happening, put spaces between the quotation mark, bracket, and full stop.

Edited By David Standing 1 on 07/12/2017 09:52:20

About 700nm.

But to attempt to be more helpfull I find the description Cheery Red more helpful. Heat it untill it gives you a nice warm feeling and makes you smile.

Just practice on some ends of silver steel.

regards Martin

Thanks chaps, that's very helpful. Reading about engineering in books is all very well but you can't beat asking someone who has done it. 'Boiled carrots' in subdued light gives me a much better idea what to aim for. And I can confirm I'm getting it right with a magnet, or by coughing up for a K-type thermocouple.

The subdued light part is awkward for me. My cluttered workshop isn't the safest place for naked flames so I usually do hot work outside. An IR or laser thermometer would solve that problem. Unfortunately the affordable models don't quite measure up to cherry red temperatures. They must exist though.

The good news about 'boiled carrots' as a temperature gauge is that we all know what that colour is. No so when 'cherry red' was chosen as the example. Modern carrots are only orange as the result of agricultural selection. Natural carrots are a nasty purple or yellow colour. As they didn't sell well, a lot of effort was put into cultivating an attractive variant.  Carrot coloured isn't really carrot coloured!

Might be an interesting project to make a thermometer capable of measuring red-heat upwards. Comparing the colour of a voltage controlled filament lamp with the unknown hot target through a magnifying glass should be easy enough. Other than buying a commercial thermometer I've no idea how to calibrate it though. Any ideas on that?

Thanks again,

Dave

Edited By SillyOldDuffer on 07/12/2017 10:35:24