Depending on the initial silk concentration, 10 ml of silk fibroin will yield 2-4 ml of concentrated silk solution after dialyzing against 10 w/v% PEG for 20-22 hours. The amount of time used to concentrate the solution may need to be altered for each batch. The concentration time is not linear, so care must be taken to avoid gelling the silk in the cassette if left in the PEG solution for too long. With experience, the researcher will be able to visually determine whether the silk is concentrated enough. If the silk is collected too early, it can either be replaced into a cassette and allow the dialysis to proceed for more time or it can be stored at 4 °C. We find that storing the silk for a few days will allow it to come to the required concentration. It is suggested that it is checked daily since the solution can gel after it has been stored for too long (approximately 1-2 weeks). The solution can be checked by attempting to use it in the intended protocol. For example, for dipped tubes a mandrel can be dipped into the solution and then it can be visually determined whether multiple beads form without coalescing. If this occurs, then the solution is not ready. The resulting silk solution should be very viscous and will appear slightly cloudy when compared to the starting solution.