There is no road map for this and getting started can be the most daunting step. Gleaning from my own experience, here's how I suggest going about it:
1) Learn the styles of marbles before trying to figure out who made them. That's the first step in narrowing down the maker. If you know it's a patch, you just eliminated several makers. If you know it's a slag, you narrowed it down to just a few. Slag, handmade, patch, swirl, patch-ribbon, solid, clearie, clay, stone, corkscrew, cateye, etc...
2) Sort your marbles by style. Put all your patches together and before long you'll start seeing similarities in some of them. The more you handle the marbles and look at them, the sooner things will start to click. Start putting together groups of similar marbles within each style, ones that look like they might be brothers and sisters.
3) What size is the marble? All the old makers made 5/8" marbles, but sometimes knowing your marble is 11/16", 7/8", or 15/16", it can help direct you to one maker over another, increasing your odds of landing on the correct maker for your decision.
4) Learn to identify the cut lines or seams of a marble. These are especially useful in identification. Most all machine made marbles will have 2 cut lines, never more. There will be the cut where the marble made before it was cut off and the marble you are looking at begins, and then the cut at the other end where the glass stream was cut off to make the marble in question. Then the marble dropped onto a set of rollers that rolled the glass into a near perfect sphere.
5) Notice what cutlines from different manufacturers look like. Different manufacturers used different machines with different cutters. Some used the same machines but had their own subtle differences or modifications that changed the mark left by the cutters. Akro cutlines are normally broad curving cut that remind me of the curvature of a man's thumbnail. Sometimes they have little streaks coming off the line and it looks like a closed eyelid with eyelashes. Learn to notice that, and you can ID an akro just by the cutline. Masters also had eyelashes, but the shape of the cutlines is different. Vitro had broad cutlines like akro, but often one side has the broad curvature of a thumbnail and the opposite cutline will be straight with little or no curvature. Peltier cutlines can have a stretched out "S" curvature. Peltier Peerless Patch cutlines can be wavy like the letter "S" or have a bird head shape. CAC cutlines are often very straight and extend 2/3 of the way across the marble. Marble King cutlines can alternate in direction from each other. The cutlines are possibly the most telling part of the marble when making an ID in most cases.
6) Notice the glass. Sometimes I see a marble and without seeing any traits other than the glass color combinations and qualities, I can instantly tell who made it. A yellow based Peltier Peerless Patch with a lime green patch... that marble has glass that is readily distinguishable at a glance. See them enough and you will recognize it from then on. Akro Agate used many types of glass, but they had some glass that almost looks like melted crayons with a high gloss. Very bold, rich coloration and sometimes Akros are IDable by glass alone. Master used a lot of dull earthy colors, translucent, clear, lackluster. Not always, but this plays a part in swaying your brain to one maker or another. Peltier had a blue and a green base glass that is pretty recognizable once you learn it and it was used in a lot of their marbles. A lot of Asian marbles have a carnival glass looking surface on them. Vitro had a purple/lavender that is pretty close to exclusive to their marbles. Sometimes it's just one thing that lends a hint to the maker, so if the seams don't give it up, maybe the color will.
7) Notice the construction and behavior of the pattern. Does the ribbon dive in and out of the marble, or lay on top? Is the patch of color just thin glass veneered over the top of a white base glass, or does the patch look like it's integral to the marble structure? Is the stream/ribbon striated or solid? Does it have ruffles along the sides in the clear parts, or is it smooth? Do the ends of the streams/ribbons have thin long points or angled off tips? Does the stream/ribbon swirl lazily or zig-zag and criss-cross? Does it look like it just looped over on itself one time or did it dribble around all over to make the marble? Does the stream start at one end and circle the marble all the way to the other end and stop? The answers to these questions lead you through a flow-chart to help determine the maker.
8) Look for surface oddities. Popped bubbles leave little craters or "blow holes". The glass cooled, the pressure in the bubble had to escape, and "POP!". Peltier is well known for having those. Most other makers, not-so-much. Does the seam or cutline have a wrinkle in the surface of the marble? Does the marble have an orange-peel texture on the surface?
Start at step one and once you have a good grasp on it, go to step 2. Some steps will be done in minutes, some may take weeks. Some marbles can never be IDed with 100% certainty. Some have traits that conflict with each other as to determining a maker and some just don't give up enough hints or have distinguishable enough traits to be able to narrow them down. The better you understand these steps and what traits belong to which makers, the higher your percentage of correct IDs will be. You can spend a lifetime studying but you will never get them all right all the time. That's the fun of marbles, you never reach a point where you quit learning.
The question of oxblood... all I can say is get one or some from someone who knows (not just ebay... tons of marbles are advertised as having oxblood but they don't). Once you see it a couple of times, it will click and then there will be no question next time you see it. The best way I can describe it is imagine if you melted a dark red brick and used a paintbrush to put it on the marble. That's what it looks like. Dried blood applied with a brush, fingernail polish, etc... It's not transparent, it's not runny or thinned out looking. Google Akro milky oxblood marbles and silver oxblood marbles and you'll see what I mean.
Sorry for the long post, but I've sorta been wanting to put this into words for a while anyway as this is a common topic for beginners looking into the world of marbles.
