Bright lines:
L-6 a high nickel content carbon steel. It is common used in sawmill bandsaw blades, but not always. It can be purchased in round stock. It combines well with carbon steel for a highly reflective, high contrast billet. L-6 is known as a tough steel and adding it to the billet will only enhance the performance.
15N20 the Swedish version of L-6. It can be bought in thin stock from Jeff Carlisle and is an excellent steel with constant quality.
O-1 is a common tool steel that has enough chrome to make a bright line when welded with low carbon or high carbon steels. It is sensitive to heat and will crumble if overheated, but by the same token can be welded cleanly at lower temperatures.
ASTM 203E is a nickel bearing low carbon steel. It is common used in making up fittings, but can be used as the low carbon element in Damascus blades. Nice contrast and high reflectivity. You can by this in sheet from American Alloy Steel Houston, TX 1-800-231-3502.
Nickel for the brightest contrast pure nickel is often used. I do not recommend it for blade steel. Nickel is a carbon blocker and in the finished billet the soft nickel layers will end up on the edge and affect performance. It is best used in fittings for really high contrast.
Dark Lines
The dark lines in the Damascus come for the low alloy carbon steels. You can get colors from light gray to dark black by varying the carbon content, the lightest being regular hot rolled low carbon. Adding low carbon to the billet will lower the overall carbon content of the finished piece of steel and you need to take it into account as you construct your billet. I like to have at least .60 to .80 points carbon in my billets and this can be figured by taking the percent carbon in each piece of the original billet and then averaging to find the projected carbon content in the finished billet. This seems like higher math to me tonight, but I am sure you can figure it out if you give it some thought. This will only represent a guesstimate since you are going to lose some carbon in the process of welding the billet. I have gone almost exclusively to high carbon billets and am happy with the performance I get, but it is entirely up to the individual maker and what effect he his looking to achieve.
Howard Clark ran a series of experiments to find out what was giving the variation in shades of gray from one carbon steel over another. His results showed that the manganese content contributed to the darkness of the line. You might contact Howard for more information on this if you are interested. If you have made any Damascus you also have found out that the heat treatment will greatly affect the etch and coloration of the finished steel too. The Japanese hamon is a great example of the wide variation possible through heat treatment. When you differentially harden a homogenous piece of steel you get marked difference in colors from the hardened portion and the unhardened. Most makers curse their etchant first, but if you think about what is going on with the steels the problem often lies in the heat treatment.
Some of my favorite carbon steels to use in Damascus are:
1095 It is a good knife steel and has a slightly higher beginning carbon content and contrast nicely with 15N20 or L-6
1084 Slightly lower carbon content and more forgiving in the heat treat. Makes a good blade steel, easy welding.
5160 A lot of makers really like this steel. It is an oil hardening steel and has been called fool proof steel because it is very forgiving with the forging and hardening. I don't use it much but not a bad choice.
52100 This is an alloyed steel and once you learn how to heat treat and forge it, it has exceptional qualities. Howard says that when they first made it they had to extend the grain size charts to accommodate it's very fine grain. It is not for the novice and you really need good controls for proper heat treating, but worth the effort in terms of performance.
W-2 This is the bladesmiths steel of choice because of it forges nicely and heat treats so well. It has added vanadium and is a fine grain steel. The only problem is they don't make it any more or at least I can't find it so it isn't readily available.
Spheroidize when done as this mix will eat up evey mill or drill you put to it if you don't.
