They are required to undergo immersion without a blessing, as decided by Maran the Shevet HaLevi (Yoreh Deah, Siman 43). The reason for this is that many authorities believe the law for glass-coated earthenware is the same as the law for iron-coated earthenware (see Issur V’Heter Rule 58, Shach Siman 120:2, Darkei Teshuva, Aruch HaShulchan in the name of the Pri Chadash, and Zivchei Tzedek). On the other hand, many hold that there is no need to immerse them at all (see Pri Toar). Therefore, Maran the Ben Ish Chai (Parshat Matot) and the Shevet HaLevi decided to immerse them without a blessing. We emphasize that, of course, if a Jew performed the coating, there is no need to immerse the vessels according to all opinions (and there are kashrut guides that have erred in this matter).