A forge has no thermometer, so this is one

A vertical bar, dull red at the base climbing through cherry and orange to pale yellow at the top. Six bands, each with a temperature and a name: 600C DULL RED, 800C CHERRY, 900C ORANGE, 1000C FORGE, 1200C WELD, 1300C TOO LATE.

Five of those are heats. The last one is a verdict.

What is this chart actually measuring?

The colour coming off hot steel, translated into a number nobody in the shop needs a dial to read.

There's no thermometer built for the inside of a forge — nothing you could hold near the fire would survive it, and a probe long enough to reach in from a safe distance wouldn't respond fast enough to be useful anyway. So the trade uses the one instrument already present: the glow. The chart is what turns that glow from an impression into a reading.

Why does the colour change at all?

Because hot steel radiates light, and the colour of that light shifts with temperature in a fixed, physical order — it isn't a convention the trade agreed on, it's how incandescence works.

Dull red is the steel just starting to move under a hammer. Cherry and orange are the working range most hand-forging happens in. By the time it reaches pale yellow it's close to welding heat, and past that it stops being steel you can shape and starts being steel you're about to lose.

Why is TOO LATE printed the same size as the temperatures?

Because at that heat, it functions like one.

1300C isn't a target the way FORGE or WELD are — it's the point past which the piece is scrap, not a state you work in. The gap between a good weld and a ruined one can be as little as four seconds, which is not enough time to notice a mistake and correct it. Printing the warning in the same type as the readings, in the same position on the same bar, is the honest version: it isn't a caption, it's the next line down.

Can a smith actually tell 900C from 1000C on sight?

Reliably, once the eye is trained on this exact bar, in this exact light.

That's the part a chart like this can't fully carry off the page — colour temperature reading is learned against a specific forge, in daylight or artificial light, because ambient light shifts how a colour looks. The chart gives the sequence and the names. The judgement between adjacent bands is built by hours at an anvil, the same way a torque figure only means something once you've felt the click.

Can I put a real smithy's name on this?

The chart itself, no problem — heat and colour are physics, and physics isn't owned by anybody.

What is somebody's property is a specific forge's printed card: their house style, their name across the top, their particular choice of which six bands to show. If a real smithy's card is the point, ask them — the permission is part of the job, the same as licensing any other business's document. If it isn't the point, the invented version is better anyway, because it can be about the hours the wearer has actually put in at their own anvil rather than somebody else's shop.

Does the same idea work outside a forge?

Yes — any trade that reads a process by colour instead of a dial ends up with something like this.

Glassblowers judge workability by the glow of the glass in roughly the same way. Kiln firing is read by colour before it's read by a pyrometer, in traditions that predate reliable ones. Welding shops watch the colour that spreads either side of a weld as a rough gauge of how hot the surrounding metal got. All of them are the same trick: a material announces its own state, and somebody learned to read the announcement.

Why not just print a flame?

Because a flame says there's fire here, and this chart says something a flame can't: exactly which heat, named, in order, with the one that ruins the work marked out from the rest.

A decorative flame is a symbol anyone can wear. A correct heat chart is a claim that can be checked — another smith looking at this bar can confirm the sequence is right, the same way a wrong wiring diagram gives itself away to an electrician immediately. That's the entire difference between the two options, and it's the whole reason to print the real one.

Does it print well?

Yes, treated as six flat swatches rather than one smooth gradient.

A soft blend from red to yellow is exactly the kind of print that goes grey and muddy on fabric — wide gradients don't survive cloth the way flat colour does. This chart already comes as six named bands with hard edges between them, which is the version that prints cleanly: each band a distinct swatch, a visible seam where cherry becomes orange rather than a fade. Keep the labels large and there aren't many other places for it to go wrong.

How do I get one made?

Describe the range at JustOG — which bands matter to you, and whether TOO LATE stays or the chart stops at WELD. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.

Designs other people have published are in the shop.

The bar runs from a colour you could hold your hand near to one that means put the piece down.