Lessons in Blacksmithing
Copyright 2002 - 2007 IFORGEIRON, All rights reserved.
LB0007 Seeing Colors
Explanation of colors:
I divide red, orange, and yellow (the colors of heated metal) into 3 groups each. Start with black then low red, medium red and high red, low orange, medium orange, and high orange, low yellow, medium yellow, and high yellow, then white heat. This is followed by sparks. The lower temperatures have more separation in heat colors than the separation in heat colors at high temperatures. The difference is suttle, and everyone sees color differently. The same colors are different temperatures in bright sun then in shade and may differ by as much as 2, 3, or 4 color levels. You need to standardize to your conditions. The 12 color divisions (black to sparks) are enough for discussion purposes, and are repeatable under YOUR conditions.
This is the time you need to find a steel yard and purchase some NEW mild steel stock. Put the metal into the fire and get it hot enough to throw sparks, just like a 4th of July (USA) sparkler. This is usually when the metal is beyond high yellow or white in color. You have now successfully burned the metal, don't do it again as that is TOO HOT. Cut the burnt end off the stock to where there is new material.
Put the stock back into the fire, heat to high orange or yellow, and hit it with a hammer. It will move a certain way under the hammer each (every) time. When the metal gets to low orange in color by loosing heat, it will stiffen a bit. Warm it back up and do it again at orange in color, hammering the metal while it falls to medium red in color. Put it in the fire and bring it only up to showing low red in color. Hit it with the hammer and feel how it moves (or doesn't want to move). Back to the fire and then repeat at yellow. Feel the hammer when it hits the metal at different temperatures. If you see the color of the mild steel as red stop and take another heat, get it back up to working temperature.
Different types of metal act differently at the same heat color. Some metals have short working temperatures, meaning that they only should be worked at medium to high yellow for instance. If it gets to low yellow quit and take another heat. This is something you will have to either learn on your own or seek the advice of others that have worked this type steel.
Your eyes see colors differently then how others see and label the same color due to age, glasses, and life experiences. You are building YOUR heat standard for YOUR forge under YOUR smithy conditions.
During the next week, look at different objects in your part of the world and âseeâ the color. Then label that color as black, reds, oranges, yellows, white. The practice will aid you when you get to the forge and being able to tell the sometimes suttle differences in colors. If you really want to know what temperature a specific color represents, or what temperature a piece of steel has been heated to, purchase a temperature measuring device called a pyrometer. There are also wax pencils that can be applied to the steel that will melt at a specific temperature. Both work well and are more than accurate for use in blacksmithing.
A temperature chart for mild steel is as follows.
Sparkler - burning the metal
Black heat (1000*F +/- down to room temperature)
Black heat can be 1000*F or more depending on the ambient lighting.
From black, to room temperature, to freezing, the metal looks the same. This is why everything on the hot table is considered hot until it goes into the water, then into the bare hand, and only then onto the work table.
The best way I have found to get a "black heat" temperature reading is to turn the hand palm up and DO NOT TOUCH but just pass the back of the hand across the metal. Start at about 6 inches or so and lower the gap with each pass. The back of the hand is not calloused but tender, and sensitive to heat.
That is 12 levels of heat. If you divide 100% by 12 that is 8% repeatability at each heat level, or about 150-200 *F