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Hello! Yes, you could (hypothetically) use hemp oil as it is also a drying oil. You will need to do some experimenting with the ratio of beeswax, to figure out what consistency works for you.
Hey! Home made egg egg tempera usually does not last very long - be sure to keep it in the refrigerator to extend its life as long as possible. You can also experiment with powdered egg to get a little bit more life out of itCommercial egg tempera paint is an emulsion with other oils to extend its life.
Mineral spirits would work great in cleaning up after this paint. Since it takes a long time for natural linseed oil to dry, you may also be able to get away with using dish detergent as well.