I wrote about working with hot sugar in my blog post Hot Sugar – Caramel Sauce – Pancakes. Before people used thermometers to make candy, people supposedly used their hands. People supposedly dipped their fingers in ice water and then put them into hot sugar. Ice water will protect the surface of the skin of a part of a hand for a moment. There are pictures of Raymond Oliver using this technique in his cookbook La Cuisine . The technique is also mentioned in a book of techniques by the Le Cordon Bleu.
I could not immediately develop a strategy to lift enough sugar from the saucepan with my fingers to determine the hardness of the sugar. I used a spoon to put sugar in the ice water, or I poured sugar into the ice water. After the sugar cools, the hardness of the sugar can be determined. If the sugar is soft, then it can be shaped into a ball using the palms of the hands.