i don't think tissue paper will work nor do i think it will dissolve in water....might be wrong tho!!
when i do string scrappy quilts ( and i do a LOT of them) i use the waxy paper that deli's use to line the food trays. i buy a box at sams or cosco for ( don't remember...the box lasts forever!! ) maybe 10.00. you can pre cut them down to size as they come out of the box about 15 inchs square and they rip off very very easy. i have used old phone books but sometimes the ink would run......
scrappy string quilts rule!!
jodi in leavenworth