There are mainly two types of glass to metal seals , one is matched seal and other one is compression seal.
A "matched glass-to-metal seal" uses glass and metal materials with similar coefficients of thermal expansion (CTE), creating a bond through chemical reaction, while a "compression glass-to-metal seal" relies on a large difference in CTE between the glass and metal, where the metal housing shrinks onto the glass during cooling, creating a tight seal through compressive force; essentially, a matched seal bonds the materials together, while a compression seal physically squeezes the glass with the metal to seal it.
