DSF

Some people find that their image blurs while the mug is cooling so they use warm water to cool them faster. The down side of using water is that it can crack or cause small fractures in the mug, the fractures may not show untill the mug has been used a bit and tea has gotten into them producing a spider web type pattern on the inside of the mug. Another option sometimes recommended on here is to use a fan to cool them, personally I haven't ever notice a mug blur while cooling so I just let them cool in their own time.

I've only had mugs blur on cooling when we got a batch of cheap 10oz standard chunky mugs, we got in for a print job for another designer - the type of mug we use for our own work don't do this, so it was a bit of a surprise to see it happen.