The opposite of soften is - harden
Soften.
soften
It will harden a stool
Most glues will get harder when heated a little. Overheating will soften them.
no
A plastic which will soften when heated and harden when cooled.
carbon,
Heat can soften some forms of matter and heat can also harden other forms.
'Glue' is too general a term for that question. -What makes some glues soften will make other glues harden. -Please be specific about which 'glue' you mean.
Depends entirely on the glue. some harden in water, some soften or even dissolve.-Name your glue -
A macaroon is actually classed as a cake, because when cakes go stale they harden, but biscuit soften when they go stale!