Connie and Mike, my local art store is called PlaZa artist supplies. They are a regional chain. I didn't mention their name simply because I'm not sure how many of them there are! [
] I mention brand names when appropriate, and when I can remember how to spell it! I use PearlEx luster powder and pigment manufactured by Jacquard(sp?) Products in my castings (http://www.jacquardproducts.com/products/pearlex/). They are the people that make the $25, 12-jar kit you mentioned. Michael's doesn't carry the big(ger) jars of PearlEx; for that, I go to PlaZa. PlaZa has a 10 or 15% off card if you shop there frequently, and I was able to get a 2nd 12-jar kit and, for its retail price, also get a big(ger) jar of "interference blue".
Some here have also used liquid dyes in their castings; I have a set from Michael's, but haven't tried them yet. My problem with the liquid is that the blank is likely to be transparent, and I like something more opaque for most of my blanks.
As for the "ribbons", they have appeared in the castings I've made all by themselves. I am pretty sure they are the pearling agent, and that it is just tending to be chemically/electrically attracted to itself. If you look here, you'll see a silver casting I made two weekends ago, and turned this weekend:
http://www.penturners.org/forum/topic.asp?TOPIC_ID=6899
I didn't do anything special with that blank, and actually thought it was going to be a relatively solid color; BOY was I wrong!
As for the Crimson Marble, you may be able to simply cast it in the resin. For example, if you do like Ed Davidson (YoYoSpin) has been doing and glue the ribbon to a tube, and then cast the tube in resin, you may be able to get the look you want.
Hope this helps, and, as always, feel free to ask questions!