First, they don’t have to be made of metal. But they cannot be made of glass, either.
From the current GIRM:
- Sacred vessels are to be made from precious metal. If they are made from metal that rusts or from a metal less precious than gold, then ordinarily they should be gilded on the inside.
- In the Dioceses of the United States of America, sacred vessels may also be made from other solid materials that, according to the common estimation in each region, are precious, for example, ebony or other hard woods, provided that such materials are suited to sacred use and do not easily break or deteriorate. This applies to all vessels which hold the hosts, such as the paten, the ciborium, the pyx, the monstrance, and other things of this kind.
Waterford does not easily break (certainly not like a cheap wine glass) and would be considered “precious.”
However RS slammed the door shut on this:
[117.] Sacred vessels for containing the Body and Blood of the Lord must be made in strict conformity with the norms of tradition and of the liturgical books. The Bishops’ Conferences have the faculty to decide whether it is appropriate, once their decisions have been given the recognitio by the Apostolic See, for sacred vessels to be made of other solid materials as well. It is strictly required, however, that such materials be truly noble in the common estimation within a given region, so that honor will be given to the Lord by their use, and all risk of diminishing the doctrine of the Real Presence of Christ in the Eucharistic species in the eyes of the faithful will be avoided. Reprobated, therefore, is any practice of using for the celebration of Mass common vessels, or others lacking in quality, or devoid of all artistic merit or which are mere containers, **as also other vessels made from glass, **earthenware, clay, or other materials that break easily. This norm is to be applied even as regards metals and other materials that easily rust or deteriorate.