1. If the crystal is stuck to a plastic plate or plastic slide, manipulate the plastic instead of the crystal. Using a needle, such as a Micro Needle, a Crystal Probe or syringe needle, stick the needle into the plastic a bit away from the crystal. Press hard and wiggle the needle enough to distort the plastic. The idea is to stretch and distort the shape of the plastic under the crystal and not touch the crystal. This movement in the plastic can free the crystal from the plastic.
2. Change plastics. Crystals are reported to stick less to polypropylene and cyclic olefin copolymer (COC) plastics. The Micro-Bridge is available in polypropylene. Some versions of the Intelli-Plate, Swissci, Greiner, and Corning 96 well sitting drop crystallization plates are available in COC.
3. Crystals grown in the presence of a gel. 0.1-0.2 % (w/v) agarose or silica hydrogel will grow inside the soft agarose gel. Therefore, they are mechanically protected and will not settle to the bottom of the sitting-drop well. When you harvest a crystal cut generously around it with a MicroTool, pick it up using a CryoLoop.
4. Employ micro seeding for better control of nucleation.
5. Carefully position a small piece of dry ice on the opposite side of the plastic from the crystal. The temperature change can sometimes free the crystal from the plastic plate.
6. Sonicate the plate to free the crystals from the surface.
7. Apply a very thin, smooth layer of vacuum grease or petroleum jelly to the plate or cover slide and set the drop on the grease.