Is a gloss finish harder than a satin finish ?
No.
The finish used to achieve all the sheens from gloss to matte
is the same.
All the finishes originally are gloss.
In order to achieve all other sheens, some chemicals
containing microscopic particles that remain in suspension in
the finish are added and the light is reflected by such
particles in different angles and in relation to the quantity of
particles in suspension in the finish.
Another way (Much more expensive because very labor
intensive) to change the sheen of a finish is the rubbing
effect. Where a gloss finish is hand rubbed with ultra fine
abrasives till the desired effect is achieved.