Dye Sublimation. This can sometimes cause blurry legends but its rare, and when it happens it never looks unbearable, simply like a blurry set of double shot keycaps. The way dye sublimation works is they make the blank keycap, etch out the space for the legend with a laser, then pour dye into the hole. They then heat the cap up so the legend stays. Overall it sounds sketch at first but I've had some amazing dye sub keycaps.
Hope this helped!!