I am experiencing success using pops rosin and rejuvenating it, when it gets stale, by using the "letting it sit 10-12 hours in 50 pct. (or 25/75 pct.) isopropyl alcohol water mixture in a Tupperware plastic container." I must say though that the real difficulty with Spiros and Pops for me and getting a "great arco sound" occurs way high up on the fingerboard hitting the high C#,D,D#,E notes on the A string as well as the high F#,G,G#,A notes on the D string. For me bowing is more difficult up there, and starting the string smoothly is the key challenge, I have to apply more tension on the string to get clear intonation at the start of the bow stroke. Also I need to bow closer to the bridge as to avoid doing what I refer to as "hitting the third rail", i.e., not cleanly bowing the single string and touch the adjacent string bowing way high up on the A and D strings. Please let me know if the other rosins get clean sounds with Spiro's way up there.