Hello Di, just seen your question, the gold size is only the adhesive in liquid form for the gold to adhere to, gold leaf comes in 2 different sheets, (1) is loose leaf which are sheets loosely held in a book,and applied with a gilders tip, a small flat brush about 3" wide and holding the gold sheet by static or slightly brushing against your cheek to get a small amount of grease off, the other leaf is fixed in the book by a small amount adhesive and has to be applied by pressing or rubbing with your thumb to the sized object.
Gold will last longer than any paint coating providing you leave it alone, it needs no attention once applied, not like the elderly lady cleaner who once polished it with Brasso and wore all the gold away, this was in my apprentice days.