How to make slime

PREPARATION

NEW NOTE: Post Apple Scientific is the place I have purchased PVA in the past. They have the powder form, and a PVA solution, which really saves time.

Both the PVA and the borax are sold as dry powders. Both need to be dissolved in water to make separate solutions. Use 40g of PVA for each liter of water, and 5g of borax per 100ml of water. This is enough for 20 people. The PVA is the more difficult of the two to dissolve. If you have a magnetic stirrer/hot plate, you can simply heat the water to about 90oC, start the stir bar, and sprinkle in the powder. If you don't have this luxury, don't attempt to mix the powder manually - it will take forever! Instead, do what I do. I use a crock pot! This is a great tool for the purpose, because at the "low" setting it keeps liquids just below boiling temperature. Simply sprinkle in the PVA powder, stir, and cover. Stir again in a half hour, and every half hour or so thereafter until the powder is dissolved. I've left the PVA cooking overnight without stirring, and no harm has been done. When the PVA is completely dissolved, there will be no evidence of particles in the water. The particles are clear, so check for them under bright light.
Ladle the solution into a labeled storage bottle for later use.

To mix the borax solution, dissolve the borax in warm distilled water. Allow to cool, and transfer to a labeled storage bottle.

DOING THE EXPERIMENT

If you are doing a classroom demonstration, things go smoothly if the solutions are distributed in the following manner. Beforehand, pour 50ml of PVA solution into the required number of Solo(tm) plastic soufflé cups and cover with the plastic lid. Get a cup of the borax solution and a dropper. Determine how many dropperfulls are required to dispense 5ml. Distribute the PVA in the sealed cups, and instruct the students to open carefully. Distribute wooden stir sticks at the same time. Allow students to decide whether they would like to color their slime with food coloring. Distribute two drops of the food coloring into each student's PVA. Have them stir the color slowly (to avoid splashing) with the stick. As they are stirring in the color, dispense the borax into the student's PVA, and have them continue to stir. When gelation has taken place, they can close the lid and shake the cup to gel the PVA on the lid of the cup. The students can take their slime home in the sealed cup. They should be told that the slime will keep for weeks in the refrigerator, but may become moldy after a week or so if left out. The slime will wash out of most clothing with detergent and warm water, but care should be taken to avoid the need to do so. The stirring sticks can be discarded in a waste receptacle.