Add 2 T. vinegar to 1/2 cup of skim milk - it has to be skim milk for this to work right. Stir it and let it sit for 5-7 minutes. The vinegar makes the curd of the milk separate from the whey. Think Little Miss Muffet here.
Put a paper towel over a cup to make a strainer. Pour the curds and whey into the paper towel to drain the whey from the curds. This reminded me of making cheese.
Scoop the curds out of the strainer and lay them on a couple of layers of paper towels. Press the curds until it forms
a dry lump like this. Put this lump in a cup and add 2 tsp. of water and 1 tsp. baking soda. Stir it around to mix well.
The mixture starts, very quietly, popping when the baking soda combines with the vinegar in the curds. Spark held it up to his ear to hear the snap, crackle, and pop.
Keep stirring until it resembles a thin paste/thick glue mixture. Add few extra drops of water may need to be added to make it the right consistency.
It worked! We made this crude Tom Sawyer raft and it is firmly stuck together.