Generally, a metal detector does not react to glass. There are situations where a metal detector will react to metal that is in close proximity to the glass and often bottles will have a metal cap or ink in inkwells. The Museum’s Chief Scientist explains lead and metals in glass:
The confusion of lead-the-metal and lead-in-glass is a common one. Because the name of the element equates in people’s mind with the element in its practical metallic form, it is assumed that some aspects of that metallic nature persists after the element is dissolved into the glass.
The lead atoms in lead glass have been reacted with, and is bonded to, oxygen atoms in the glass structure. It has ceased to be “lead the metal.” It is then more closely thought of as lead oxide dissolved in glass. A metal detector cannot detect it. Those devices depend upon sensing electromagnetic feedback from materials that have some significant amount of electrical conductivity. That property, the ability to conduct electrons, is lost from the lead when it combines with the oxygen in the glass.
Image: Example of a lead glass vessel. [Romer. George Ravenscroft, Glassmaker. Savoy Glasshouse. London, England. About 1676-1678. CMoG 50.2.2.]
The same is true of the other constituents of glass that, as elements, are metals (ex., sodium, calcium, aluminum, and iron in sodalime glass): when combined with oxygen and silicon and fused into glass, that metallic, electrical conductivity is lost, and the glass becomes a strong electrical insulator.
The same holds for any available glass: they are not sufficiently electrically conductive to respond to the signal from a metal detector.
There are examples of glass that do contain metallic elements where the metal stays a metal. So called “Aventurine” glass contains copper in small individual pieces that precipitate from the molten glass, and are distributed throughout. Copper can also be fused into a piece of glass as wires or foils. Gold foils, also, are often applied to the exterior of pieces as decoration, and sometimes cased over with clear glass. I do not know if there is typically sufficient metal in/on such pieces to be sensed by a metal detector.
.... In general, if the metal is more than a few grams and attached to the glass, the detector should detect the metal. Although, note that it isn’t seeing the glass, just the metal that is near or inside the glass.
