Bry,
Flat ground steel comes in all types: low carbon, medium carbon, high carbon, and alloy (tool steel being alloyed medium or high carbon steels). Spark testing (as recommended by Andy) can separate out low, medium, and high carbon steels (and someone with a really good "eye" can get you within 5% of carbon content), but it will not tell you the other alloying agents. To get that, you must have the part tested on a spectrometer (and most high quality foundries have such a beast these days) and then wander through a list of steels by content to figure out your alloy.
It depends upon what you need to do with the stock. If you are just going to harden and temper it generally, then a spark test is sufficient. Heat it up until a magnet is no longer attracted to it (this means that you have passed the Currie point temperature-wise) and quench it. Draw it to temper in the traditional blacksmith's fashion. However, if you need to get the most out of the properties available to you, then you need to do the spectrometer test, look up the specific (set of) alloy(s), and find the processing information on that alloy (set). Quenching (say) S7 tool steel in brine is going to lose most of the shock resisting characteristics one normally purchases S7 tool steel to get.
As you said your intent is to make cutters, I would assume that you want more than "merely" hardened steel. Doing a brine quench on steel designed to use a less-intensive quench (oil or air) will make for a more brittle finished part (cutter). This is not a "good thing." I normally cryo-quench cutters. A container of dry ice and (methyl) alcohol makes a decent cryo-quench (cool the part to 360°F/180°C until it is consistent all the way through and then dump into the cryo-quench) -- not as good as liquid nitrogen, but sufficient for most such tasks. This will make the tempering much more effective in terms of relieving stresses in the hardened part. This type of process is (for the most part) reserved for air cooling or oil cooling steels (and most effective on air cooling steels).
The suggestion (I forget who made it) of marking your steels with a Sharpie marker is spot on. What I do is (A) clean my steel bar with acetone to get the gunk off, (B) treat the surface with phosphoric acid (Naval jelly), (C) mark my steels according to the ASTM color stripe standard, and (D) wax over the whole think with a hard clear wax (Treewax brand furniture wax does a nice job). I have steel in my rack that has been there for 20+ years without any rust building up in an area where, as Ken Kesey wrote in Sometimes a Great Notion, "You can watch a keg of nails rust before your very eyes" (western Washington State).
