This is an old revision of the document!
Mix water and 寒天, cook until dissolved, strain (here it actually matters!) into sugar. Bring to 103° (that's quite fast!), then add colouring and pour int baking sheet. It should solidify quite quickly (maybe a few hours), then cut or stencil and let dry (minimise humidity) for 4-5 days
I overdid it with the temperature last time, so after 12 hours it already started to crystallise and was done in a day.