How do you clean the inside of old jugs?

Warm water and a mild detergent work best for most ceramics. Avoid harsh scrubbing brushes that scratch the glaze. For silver pieces with heavy tarnish inside, a silver dip is sometimes necessary. Rinse it thoroughly afterwards to remove chemical residue.

I found a jug that looks like silver but it has some copper showing through on the raised parts of the handle. Is this normal?

That sounds like Sheffield plate or an early electroplated piece. The silver layer is relatively thin and rubs away with use over the decades. The copper base metal showing through is called bleeding. Many buyers look for this as it shows the piece has a genuine history of use.

Can I still put hot milk in these?

Antique silver and thick ironstone cope with heat well. Delicate bone china needs care. Sudden changes in temperature cause the glaze to craze.

My grandmother gave me a small jug with a blue and white landscape pattern printed on it. It seems to have lines all over the clear glaze. What causes that?

Those fine lines are called crazing. It happens when the ceramic body and the clear glaze shrink at different rates during cooling in the kiln. It is common on nineteenth-century earthenware. Moisture sometimes gets under the glaze and causes minor staining, but the piece remains structurally sound.