I can only answer froom my experiences. I use flat crepe pre hemmed silk scarves from Dharma Trading so it will show on both sides. It is still slightly darker on the front, but does show on both sides. The silk satin felt nicer, but as you said, it only showed the pattern on the front side.
You didn't say, but i assume you are putting the scarves in an alum solution first. I let them soak in the solution for at least a half hour, then spin out the excess in my washing machine and let them hang to dry, then iron them before marbling to get rid of any creases.
I've been experimenting with using vinegar in my rinse in the washing machine because that is supposed to make them shinier and it does seem to help. Golden makes a GAC 900 for fabric, but I didn't find that it made any difference.
When I lay them in the marbling tank, I do run my finger around the edges to make sure they get printed, then I rinse them in two buckets of water and hang to dry for 24 hours. I try to marble outside as much as possible because when I do it in the house, I have to put towels down everywhere, but it's too cold of course in the winter time here to do it outside after September.
After I let them dry, I heat set them in a drier with an old pair of jeans or a towel so they don't tangle so much for a half hour, then wash them in the washer on a short, delicate cycle and dry them again. I have also tried ironing them to heat set them before washing them. I would be concerned about putting them in the oven.
I do a large number of scarves, so have switched to using methyl cellulose because the carageenan goes bad so quickly here in the summer - it gets to 90, believe it or not.
I have used several brands of paints, most work.
I do have problems with them tangling in the washing machine. I've tried net bags and several other things, but they still do it. I spray them with a water misting bottle on the creases, then use a spray sizing and they seem to be fine. I have not experience a problem with permanent creases in the scarves. I use a hot steam iron on them also. The marbling has never come off in the machine. Because I'm doing a high volume of them, I don't wash them by hand, and also want to make sure they are not going to fade any further after they leave me is the other reason why I do them that way.
The only way the marbling would come off is if you didn't use alum or used too weak a solution of alum would be my opinion.
So far I have been unsuccessful in marbling on stretched canvas - if anyone has any suggestions, I would be glad to hear them. I also experimented and marbled on some 4 x 4" travertine tiles, and they worked fine without alum, also some white polyester ribbon worked well without alum.
Don't know if Iris or Pat will contribute their views, Hope this was of some help.