Melt the sugar in cold water, add the glucose, and when dissolved boil up and skim, and place the lid on the saucepan for a few minutes. When the syrup is boiling at its own level, put in the thermometer and boil it up to 240 degrees. Sprinkle the slab with warm water, pour the syrup on it, and again sprinkle with water to prevent a crust forming. As soon as the syrup has slightly cooled (it should crinkle up when touched at the edge with the finger), gather it up with the scraper into a heap; then work it evenly and smoothly with the spatula until the whole becomes creamy, and finally opaque and solid. Knead it smooth with the hand; cut off and colour a portion, working in the colour on the slab before adding the essence. Place in a small saucepan with a little water, and melt to the consistency of thick cream.