I purchased slate coasters from Amazon and wanted to know the best setting to engrave. I did not want to waste coasters, so I set up a test grid. I kept finding "How-tos" on how to setup a test grid. I wanted to post the design file I made so you don't have to make your own. I would imagine you can use this on any material. You may want to resize it to fit whatever you are testing.
You can use my design file to do the exact same settings. My test ranges from Power: 10 - 55 and Speeds: 20 - 250.
Once you finish engraving, look at the material to determine the best setting for your liking. On this specific coaster, we decided Power: 25 and Speed: 175 were the best settings. We thought this was the best setting considering Power and Speed. The upper-left side is too light. The lower-right is bulging and scorched. You can decide what you like best.