Smoke Patination

The glass is smoked forming a thin layer of carbon soot. It is then fixed by various means depending on the desired outcome and water gilded. It can produce a soft dark patination or a speckled broken texture.

Lay the glass flat so that you can access it underneath (I haven't found a way to use this on shop windows because it doesn't work with vertical glass). Get a candle with a very long wick and hold it at sufficient distance so that the flame deposits the soot on the glass. It shouldn't be so thick that you can't see through it, just a tinting layer. You could also use a rolled up piece of newspaper. The carbon deposit forms black swirl shapes which can be fixed or not fixed depending on your requirements.

12 carat white gold, fixed