To be honest, I'm not sure if it is fully purged. 4 hours is a really short amount of time I think especially for a natural evap. It sitting it will do that, the problem is, if it isn't properly purged the ISO will be stuck in it until you purge it out. The color does look nice though.
With me, how I get shatter is, after the ISO is fully evaped (can't smell it, you flip the pyrex over and nothing happpens) I then put it in a hot water bath for 20 mins. I then pull it out, wait a minute or so and scrape away. Works out pretty wellish for me. Other people get shatter with no heat what so ever.