10 g of powdered CaCO3 are slowly added to a stirred solution of 25 g FeCl3.6 H2O. in 100 ml H2O. The resulting dark brown solution is placed into a dialysis cellophane tubing, that is suspended in a container with distilled water. The water is changed at 24 h intervals for 4 days. The dialysis can be performed with parchment (attach to the end of a bottomless tube) or from animal guts (obtained from a butcher or also found in drugstores, sold as prophylactics). Concentrate the solution to its original volume from a large dish at room temperature or using a haidryer. Pour some of the solution into a small round flattened bottle, add a tiny amount of NaCl and shake well. Leave untouched and see if it has jelled. If not, add more salt. The setting quality of the gel can be adjusted by varying the solution concentration and the amount of salt added. Thixotropic sols will equilibrate after one or more months, and may gel incompletely. The addition of a very tiny amount of NaCl should restore their original behaviour. The use of a K2CO3 solution instead of solid CaCO3 also seems to improve their stability in time. The addition of stabilizers such as fish glue is being investigated.