We recently did a project in which we made a potato mummy. We actually did this to study chemical reactivity and not because we are studying Egypt but it was fun none the less.
A smaller potato, peeled and cut in half. Pick a potato that will fit in the plastic cups you have on hand.
Mix 2/3 cup of table salt and 2/3 cup baking soda. This is a dessicant, like those little "pillows" you find in some packaging, like pepperoni. A dessicant is a drying and preserving agent. The ancient Egyptians used natron, a naturally occuring mineral composed mostly of soda ash. It had many other uses too, mostly in cleaning products and soap making.
One of the potato pieces was covered entirely with the "natron". The other was just set in it's cup. they are placed in a cool, dark place for a week. Those potatoes look Spark-a-licious.
After a week both potatoes are removed from the cups, the preserved potato was cleaned off a little.
The preserved potato is much lighter and is becoming hollow. The preserving salt is dicolored and damp. The potato looks pretty gross but it isn't slimy or moldy.
The non preserved spud has a little white and orange mold on it. The untreated potato would probably look worse but they were stored in the basement where it is pretty cold in the winter. In the pictures you can see that the treated potato is not rotting, it's just drying out. The point of the project, regarding reactivity, is that when moisture, heat and light are limited the potato is less able to mold and decompose.