Gtechniq Crystal Serum Light High Quality Deep Gloss Ceramic Coating - (50ml) WITH 2 FREE TOWELS! Gtechniq Crystal Serum Light (CSL) is a high quality coatings that will add an unbelievable amount of gloss, depth, and protection. It is so strong that right after you apply it you can't remove it with traditional polishes you would need to wetsand it. CSL was designed from the same DNA as the incredibly popular, but professional only Gtechniq Crystal Serum. The original Crystal Serum professional coating boasts a 7 year guarantee from Gtechniq and they took it upon themselves to make an easier to apply consumer product, which is Crystal Serum Light.