Top: shellac and baking soda.
Middle: shellac, baking soda and powdered eggshell.
Bottom: shellac, baking soda, powdered eggshell and vinegar.
3/15/18 Waiting to see how they harden.
After one day they all became very hard. Great stuff, except for the one with vinegar, it was a bit brittle. And…
After leaving the other two in water overnight they turned to goo. (Top) Shellac with baking soda. (Bottom) Shellac with baking soda and powdered eggshell.
The shellac-only layer stood up well to the same test. It was only slightly softer, it didn’t turn to goo.