Sorry for coming in here with little chemistry knowledge and a pretty inane question, but my googling skills have completely failed to cut through the enormous combined output of the baking brigade and all the lovely people making lovely things with this stuff. Unsurprisingly not one of whom has paused to mention what's actually happening on a chemical level.
For the uninitiated, salt dough is made by mixing half a part table salt with one part wheat flour, and one half to one part water, though recipes vary greatly. This is then moulded into the desired shape and baked in an oven at anywhere between 60 and 180 °C, resulting in a hard and surprisingly tough (to me anyway) finished article which is often used as a decoration on Christmas trees. But what is actually happening?
I can guess at something involving the re crystallization of the sodium chloride, but wheat flour, whilst being so incredibly common, is to me a completely incomprehensible mix of proteins, starches and all manner of other stuff. All of which involves chemistry way over my head.
I would greatly appreciate an explanation of what's going on in this hardening process.
Answer
What you get is a polymeric (starch) composite, with salt as inorganic filler.
The salt particles give toughness to the resulting composite, while the starch phase, which is just the same as in your bread, minus the unnecessary blowing agent (baking powder, yeast, whatever), connects the particles in an elastic, flexible way. You get a material that is nearly as hard as a piece of rock salt, but much less brittle.
(Elastic here means more elastic than salt. Dry bread is quite flexible, compared to rock salt ;-) .)
See also https://en.wikipedia.org/wiki/Composite_material
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