RSA™ vials, both amber and clear that are supplied with the write-on patches are ceramic and NOT an epoxy paint.
Lower quality vials are supplied with painted patches using epoxy paint, to keep the cost lower but the problem with it is they can out-gas while in the packages which causes contamination for some. If you use a non lab marker on epoxy paint, it can smear and rub off. If you write on the ceramic patches, they will not smear.
Also, the patch is permanent and will not come off under any conditions even when being put into liquid nitrogen storage. They are impervious to any solvents or alcohol.