After pouring an irreversible hydrocolloid impression after waiting for more than 15 mins. The stone cast looks chalky on the surface

After pouring an irreversible hydrocolloid impression after waiting for more than 15 mins. The stone cast looks chalky on the surface:

OR

After pouring a master cast for alginate impression have chalky occlusal surface appearance why:

1. Dehydration of alginate impression ***

2. Formation of exudates on surface

3. Slurry water

4. 1 or 2