Decorative glass of the nineteenth and twentieth centuries sometimes used etching to produce a frosted pattern. The two common methods are sand-blasting and acid-etching.
Acid etching was usually done in two stages. Firstly the whole glass is etched to a matt finish. This is followed by a different type of acid-etch to bring back some areas to a clear finish.
Sand-blasting is done by pressure-spraying a fine abrasive onto the glass. Usually the pattern in the glass is made by masking off the clear areas with a protective film. Acid etching is rarely done these days for safety reasons but it does have a softer, more pleasing appearance than sand-blasting.
Gilding over these etched areas will have a matt finish regardless of the gilding method used. The signwriters use of matt centres in lettering was originally in emulation of etched glass. The technique often being used in pub mirrors.
Water gilding on the etched glass is feasible but the gold tends to wear of the high spots easily. It may require an additional gild especially if the etching is deep. I would use it if a bright gild is also required on the surrounding non-etched areas but otherwise prefer to use oil-gilding.
Oil gilding is easier because it covers the texture better and it uses less gold.
Simply paint the etched areas with goldsize and gild as per usual.
On sand-blasted (recessed) etching, any goldsize that has flowed over the edge can be removed afterwards. Tightly cover a flat cork block with a layer of fine cloth, damped with metho (alcohol) and wipe over to remove excess size/paint/gold and restore the edge.
As with other textured glass, angel gilding and hand-silvering is suitable for gilding etched glass