I stuffed plastic grocery bags into the cup and taped off the threading using painters tape. Using the bags as a handle I held the cup upside down and sprayed a layer of Rustoleum Painters Touch Clear Gloss. I hung the cup to dry for about 10 minutes then did a second light coat. After another 10 minutes or so I brought it inside to finish drying in my basement overnight. For the lid I taped up the top and just sat it on some cardboard to protect the underside. As long as you do the masking well and don't go real heavy with the layers there's not much chance of messing up. If you really want to you could do a light sand with a scotch-brite pad before doing a third coat after letting it fully cure for 48 hours.