Some books recommend that you use this instead of Carageenan in marbling. If you live in really hot humid areas, it does keep better than Carageenan without refrigeration, and it is a little less expensive. In our experience, beginners sometimes have a more difficult time floating the paint on Methocel - it takes practice! We have experienced Marblers who will only use this, and experienced Marblers who will only use Carageenan. So try both and figure out which one works best for you!
Most instructions say to gradually add 1-1.5 oz to each gallon of room temperature water while stirring, then slowly stir in one tsp of household ammonia (not the sudsy kind). Allow to rest 20 minutes, stir again, then use. One of our experienced customers says she gets clear lumps that way. She had better luck with boiling water - pouring that into a bucket, gradually stirring in the Methocel like if you were making Cream O'Wheat (remember that stuff!) and then adding the rest of the water you need cold to cool the whole thing off, stirring all the while of course. She said it is always lump free this way. Again, see what works best for you!