How long will it take for the scientific experiment of milk key chain to be finalized?

The scientific experiment of milk key chain takes 30 minutes to finalize the design. Write on white paper with milk first. When the milk is dry, bake the white paper on a candle for 30 minutes, and the original words will be displayed. Principle: Milk contains carbon, which can be turned into black carbon when baked under candles, so that fonts will be displayed and more scientific experiments will be carried out.