The traditional veladora is made from glass. It has a circular base that slightly opens up as the outer surface extends to the mouth. The shape of the mouth allows the mezcal to “breathe”, and when someone takes a sip of mezcal from a veladora, there’s little risk of the strong alcohol fumes overwhelming them.
The veladora is convenient as well. The ribbed outer surface makes it easy to grip, and its shape makes accidentally breaking one fairly difficult. It’s also compact enough to travel with.
Originally these glass cups were used in Catholic churches to hold prayer candles. That's why you will find a crucifix imprinted on the base of each glass - to remind you of its original purpose. Someone had the great idea of borrowing the candle holder from the church to drink mezcal and a whole new category was born. Today you find the veladoras both in churches and bars in Mexico.