Heat Treatment · Heat Treat

Tempilstik

A Tempilstik is a crayon that melts at a set temperature to confirm a surface has reached heat. It is a useful cross-check for forging and hardening, but it reads surface temperature only and cannot replace a thermocouple or oven.

StageHeat TreatRank#25

Specifications

At a glance
Type	Melting-point crayon
Use	Confirm surface temperature
Range	About 40–1,000 °C by stick
Surface	Clean, scale-free steel
Reading	Mark melts and glosses
Limit	Surface only, not a soak

Technical parameters

Typical values for this class of tool
Common ratings	650 / 800 / 850 °C
Accuracy	About ± 1 % of rating
Application	Mark when cool or warm
Reading method	Visual melt point
Surface limit	Surface, not core
Interference	Scale and oil block the mark
Use case	Cross-check, not control
Shelf life	Long if kept clean

Heat TreatmentBeginner$ typical cost

Overview

A Tempilstik is a temperature-indicating crayon that melts at a specific rated temperature. You mark the steel with the crayon while it is cool or warm, then heat it; when the mark turns liquid and glossy, the steel has reached that temperature. In bladesmithing, Tempilstiks are used to confirm forging and heat-treat temperatures without relying on color, which is affected by ambient light and by your own eyes. They come in a wide range of rated temperatures, and you choose one to match a target, such as 800 degrees Celsius for an austenitizing check.

When choosing, pick the rated temperature to match the step you are checking and understand the limits. A Tempilstik indicates a surface threshold, not a soak, so it tells you when the surface reached temperature, not whether the core has equalized. It also only works on a clean surface; scale, oil, and coatings interfere with the mark. Reading color is unreliable in bright light or for people with reduced color vision, which is exactly where a crayon earns its place. The rated temperature is fixed per stick, so most smiths keep a few values on hand for different steels and steps.

In the workflow a Tempilstik is a cross-check, not a primary control. It is useful when you are learning to judge forging and hardening temperatures, when the shop lighting is poor, or when you want to confirm that an oven or forge is actually reaching the temperature it claims. It does not replace a thermocouple or a controlled oven for critical work, because it cannot hold a temperature or report how long the steel has been at heat. Used alongside color and a magnet, it helps a beginner build a reliable sense of temperature, and it is a quick way to sanity-check equipment.

Where it fits

This tool belongs to the Heat Treat stage of the build.

ForgeShapeGrindHeat TreatFinish

Safety

Before you use thisRead the manufacturer’s instructions. The points below are the hazards that come up most often with this class of tool.

Use tongs and gloves when marking hot steel, and keep the crayon away from the flame so it does not ignite or melt early.
Do not rely on a Tempilstik alone for hardening; it confirms surface temperature only and cannot tell you the core is ready.
Work in good ventilation, since some marking crayons give off fumes when they contact hot steel and burn off.

Using it well

Mark a clean, scale-free spot so the crayon melts visibly; oil, scale, or coating stops the mark reading correctly.
Use the crayon as a cross-check against color and a magnet, not as your only temperature reference during hardening.
Keep a few rated temperatures on hand for different steels, and label them so you do not confuse the sticks.
Remember the mark shows surface temperature; give the steel a moment for the core to catch up before quenching.

Compatible steels

Steels this tool is commonly used with, and which suit its working range.

1084 1095 5160 80CrV2 W2 O1

Related processes

NormalizingHardeningTemperingAnnealing

Educational reference. Forge & Anvil is an independent information resource and does not sell tools, steel or knives. Specifications and temperature ranges quoted here are typical values for the category of tool described and vary between manufacturers — always work from the documentation supplied with your own equipment. Nothing here is professional safety, legal or engineering advice.