Start by taping off any areas where you do not want resin. I usually buy powder coated tumblers and skip the painting step. I also like to buy them with the lip unpainted. I find that some products are not food safe so keeping those away from the lip is always a priority for me. So, I taped off both the unpainted top and bottom.
Mix your resin according to the package directions. Be sure to wear protective equipment at all times when working with resin.
Then adjust the Spin It for your tumbler size and add the tumbler to the machine. Make sure it is on there straight before beginning. Then start spinning the tumbler as you add the resin. For the first layer, add in the white glitter and mix well. Then start dripping it onto the top 1/4 of the tumbler. Spread to the edge with the stir stick. Then spread into a nice and even coat. Repeat with each color working your way from lightest to darkest.
I like to also lightly go over the resin while it is wet with the stir stick from left to right. This helps to distribute the glitter evenly. Continue spinning the tumbler the entire time as you don't want the resin to pool or drip off.
I used a kitchen torch to pop any bubbles but you can also use something like a lighter. I also like to use a wet paper towel or rag to remove as much excess as possible from the tape. This will make it easier to remove.
Once your tumbler is fully coated, let it spin about 30 minutes or so then remove the tape from both ends. I always look at my leftover resin in the cup to see if it is set before removing.
Stop the spinning for as little time as possible when removing the tape. Use a wet paper towel or rag to remove any resin that seeped under the tape. Then continue to spin for a couple of more hours. You can turn off the spinner after that but leave on the machine overnight to cure.