Anatometal Opal Heart End Color: White Opal 18 gauge *I usually wear 20 or 18 gauge, so I believe this is 18 gauge. I don't have the original receipt, so I can't say for sure, but it was quite expensive, so I believe it's K18. Looking at the official website, the opal end settings are only K18, so it's likely K18. In the unlikely event that the material is different, returns and exchanges are not accepted. I've taken photos indoors with a light, so the opal's color is clearly visible, but when worn outside during the day, it's more milky white with the beautiful iridescent colors unique to opals. I've used it for a short period of time. It has been sterilized, but it is a used item, so please understand. Material: K18 Scratches/Discoloration: None