Pine is a very general term used for Softwood, that is any coniferous species of tree. NOT soft wood.
It varies greatly according to species and also rate of growth. It's graded from 'construction' grade to very close-grained
knot-free stuff that you could make a violin from.
It's great if you want exploit the texture of the rougher stuff and show all the knots and fissures. Wire brushing will tear out
the softer parts between the harder rays and produce the 'driftwood' effect.
The more refined grades are fine for moulding. It's cheap enough to cut around the odd knot. It's often finger-jointed which
is OK if you are going to bury the joints in gesso or paint. The more ancient members here will remember the Lira range of mouldings
imported from Czechoslovakia before the fall of communism. I had 3m lengths of that with 10 finger joints.
It was a pain to
cut and join but you ended up with a very strong frame.
One thing to watch out for with Pine is the moisture content and dimensional stability. If it's stored in an unheated place in winter
it needs to more moved to a typical indoor warm room for a few days before you cut and join. It will shrink laterally and if you join
a wide piece straight from a dampish environment the corners will gap on the inside. This is why your shed door sticks in the winter.
Obeche is a Hardwood, botanically speaking. It too suffers from shrinkage according to moisture content, but not quite as bad as Pine.
It is more vulnerable to accidental dents than Pine. Some lengths can be very soft, almost like Balsa wood.
Old gilded frames where mostly made with a pine carcass. Some used very ropey stuff which was buried in ornaments and gesso.
You will often see old frames with enormous shrinkage cracks.