Steel Tempering Colors Chart (°F and °C)
Quick answer
Tempering colors are thin oxide films that form on clean, bright steel as it reheats after hardening: pale yellow to straw at roughly 390-430°F (200-220°C), dark straw near 460°F (238°C), brown near 490°F (254°C), purple at 520-540°F (271-282°C), and blue at 560-590°F (293-310°C), fading to pale gray-blue by 610-640°F (321-338°C). Knife edges are usually drawn to straw, cold chisels to purple, and springs to blue. The colors only read true on freshly ground or sanded steel, and time at temperature matters almost as much as the peak number. For knives, skip the guesswork and run two 2-hour oven cycles at a verified temperature instead.
What tempering colors tell you
Fresh off the quench, hardened steel is at its maximum hardness and its most brittle - stressed enough that a dropped blade can crack like glass. Tempering fixes that: you reheat the steel to a modest temperature, usually between about 350 and 650°F (177-343°C), trading a little hardness for a lot of toughness. The full hardening-and-tempering sequence is covered in heat treating knife steel for beginners.
The chart below is the classic shortcut smiths have used for centuries. As bright steel heats through the tempering range, a thin oxide skin grows on the surface, and its color marches through a fixed sequence: pale yellow, straw, brown, purple, blue, gray. Each color corresponds to a fairly narrow temperature band, so you can judge temperature with nothing but clean steel and daylight.
Hotter means softer but tougher. A razor or knife edge gets drawn only to pale straw, keeping hardness in the low 60s HRC on a steel like 1095. A cold chisel that has to survive hammer blows goes to purple. A spring that must flex without snapping goes to blue. The table gives consensus temperatures in both Fahrenheit and Celsius, along with the tools traditionally tempered at each color.
| Color on bright steel | Temp (°F) | Temp (°C) | Typical tools drawn to this color |
|---|---|---|---|
| Faint to pale yellow | 390-430 | 199-221 | Razors, scrapers, engraving tools - maximum hardness |
| Light straw | 440-450 | 227-232 | Knife edges, drill bits, taps and dies |
| Dark straw | 460-470 | 238-243 | Knife edges needing more toughness, punches, dies |
| Brown / bronze | 490-500 | 254-260 | Axes, wood chisels, drifts, shear blades |
| Purple | 520-540 | 271-282 | Cold chisels, center punches, hammer faces |
| Blue | 560-590 | 293-310 | Springs, screwdrivers, wrenches, gears |
| Pale / gray blue | 610-640 | 321-338 | Saws, spring temper in thin sections - softest useful temper |
Why the colors appear (and why the steel must be bright)
Tempering colors are not glow. They are thin-film interference, the same physics as the rainbow sheen on an oil slick or a soap bubble. As steel heats in air, a transparent iron-oxide layer grows on the surface. Light reflecting off the top of that film interferes with light reflecting off the steel beneath it, canceling some wavelengths and reinforcing others. The film thickens as temperature climbs, so the reflected color shifts in a fixed order: yellow around 400°F, brown near 490°F, purple in the low 500s, blue by about 560°F.
Because the effect depends on that microscopically thin film, it only works on bright, freshly ground or sanded steel. Mill scale, forge scale, oil, or old bluing will hide or distort the colors completely. Sand the area you care about to a clean 220-grit-or-finer finish and wipe it dry before you apply heat.
Alloy content shifts the bands too. Chromium-rich steels grow oxide more slowly, so stainless shows its colors at noticeably higher temperatures than this chart, and the tints come in weaker. The chart is calibrated for plain carbon and low-alloy steels such as 1084, 1095, 5160, and W1 - the steels most beginners are working with anyway.
Color tempering vs oven tempering
Color tempering - heating slowly with a torch or over the forge until the right tint reaches the working edge, then stopping the heat - is fast and traditional. It shines for struck tools. Hold a polished cold chisel with the bright side up, play a torch on the body, and watch the colors run toward the edge like a tide: yellow arrives first, then brown, and when purple just reaches the cutting edge you cool the tool. The edge lands at chisel hardness while the struck end stays a tougher blue. The whole job takes minutes and needs no oven.
The weakness is precision. Color tells you the surface reached a temperature for a moment; it says nothing about how long the core soaked there. For anything with a thin, hard cross-section that must hold an edge - knives above all - use an oven temper: a kitchen or toaster oven set to the target temperature and verified with a separate oven thermometer, because factory dials commonly read 25-50°F off. Give the blade two full cycles and let it cool to room temperature between them.
Typical oven settings for common knife steels land between 350 and 450°F (177-232°C) depending on the hardness you want. The heat treat and quench calculator gives starting numbers for popular steels, and the 1084 vs 1095 comparison shows how two similar steels respond differently to the same temper.
Why knives get two 2-hour cycles
One temper is rarely enough for a knife. When you quench, not all of the steel transforms to hard martensite; a fraction of softer retained austenite stays behind. During the first tempering cycle some of that austenite destabilizes, and as the blade cools back to room temperature it converts into brand-new, untempered, brittle martensite. Metallurgy references from Knife Steel Nerds to the ASM heat-treating handbooks make the same point: the second cycle exists to temper the martensite the first cycle created.
Two hours per cycle is the knifemaker's standard because tempering is a diffusion process. Temperature does most of the work, but the steel needs genuine soak time for carbon to migrate, and a thin edge and a thick spine need time to equalize. Cool the blade fully to room temperature between cycles - a water rinse is fine - because the austenite-to-martensite conversion happens on the cooldown, and skipping it defeats the purpose of the second cycle.
A practical schedule for a plain carbon blade: quench, wipe off the oil, temper at 400°F (204°C) for 2 hours, cool to room temperature, and repeat. Compare the result against the hardness expectations in the knife steel comparison table before deciding to move your next temper 25°F up or down.
Get quench and tempering starting points for your steel
Tempering colors vs forging colors
Do not confuse this chart with the glowing colors you see at the anvil. Tempering colors are reflected light from an oxide film on steel below about 650°F (343°C); the steel itself is dark. Forging colors are incandescence - light the steel emits because it is hot - and they only begin around 1,000°F (538°C), with the first faint red visible in a dim shop. By working heat the steel glows orange to yellow at roughly 1,800-2,100°F (982-1,149°C).
The two scales never overlap. The same piece of steel can show a blue temper film at 570°F and, hours later, glow cherry red at 1,500°F during rehardening. Hardening temperatures for common knife steels sit at 1,450-1,550°F (788-843°C), far above every color on this page - which is why you harden first, then temper as a separate, cooler step.
For the incandescent scale, see the forging temperature table or the interactive forging temperature chart.
Frequently asked questions
What temperature is straw color on steel?
Light straw appears at roughly 440-450°F (227-232°C) on bright carbon steel, with the first pale yellow tint starting around 390-430°F (199-221°C) and dark straw arriving near 460-470°F (238-243°C). Straw is the classic draw for knife edges and cutting tools that must stay hard, because it relieves quench stress while giving up very little hardness.
What temperature does steel turn blue?
Full blue develops at about 560-590°F (293-310°C), with dark purple just below it and pale gray-blue following at 610-640°F (321-338°C). Blue is spring temper: excellent flex and toughness, but too soft to hold a fine cutting edge. That is why springs and saw blades are blued and knife edges are drawn to straw instead.
Do tempering colors work on stainless steel?
Not reliably. Chromium slows surface oxide growth, so stainless steels show interference colors at higher temperatures than carbon steel, and the tints are weaker and shifted. For stainless blades, skip color judging entirely: temper in an oven at the temperature the steel's datasheet specifies, verify with a thermometer, and expect two or even three cycles.
Can you temper a knife in a kitchen oven?
Yes. Most carbon steel blades temper at 350-450°F (177-232°C), squarely inside kitchen oven range. Verify the real temperature with a separate oven thermometer, since factory dials are commonly off by 25-50°F, and run two 2-hour cycles with a room-temperature cooldown between them. Keep the blade on the middle rack, away from the heating element.
Why did my blade edge turn purple while grinding?
Friction pushed that spot past roughly 500-540°F (260-282°C), so the thin edge locally over-tempered and lost hardness. If a hardened edge shows purple or blue, expect a soft spot: grind past it or re-harden. Prevent it by grinding cooler - fresh belts, light pressure, and a dunk in water between passes.
What is the difference between tempering colors and forging colors?
Tempering colors are a thin oxide film reflecting light on steel below about 650°F (343°C) - the steel is not glowing. Forging colors are emitted light that begins as faint red near 1,000°F (538°C) and runs through orange and yellow toward welding heat around 2,300°F. See the forging temperature table for that scale.
Last verified 2026-07. Specs, sizes and market prices change - confirm details on the retailer page before buying.