it's a combination of butyl cellosolve, butyl carbitol, and acetone. i've made the basic formula noted in the msds sheets.. but lately i've preferred to drop the cellosolve all together from the recipe. i think they use the cellosolve to simply keep the cost down. butyl carbitol is about $54 a gallon vs. butyl cellosolve at $28 a gallon. the more carbitol i've used the better the results. (cellosolve on it's own can cause mild coagualtion. carbitol on it's own turns the ink into silky fog)
currently i use 6 parts butyl carbitol 1 part acetone. before using this on your ink, do a small test for miscability and coagulation on a piece of aluminum foil. ...just in case you have some odd properties in your ink. one note about the butyl carbitol, it's very very very slow drying or almost "not drying" by putting some of this directly on the head platen (no acetone) or cap tops, it will render that area "undryable" if you are doing maintenance.