Agate Burnisher tool is what you need to burnish the gold leaf. The agates are semi-precious stones that are formed from silica compounds. They contain variations in the colouring. Homogeneously structured agates are banded with a metal ring/handle and used for burnishing. The agates must be deaden in order to use for burnishing. They are very sensitive to scratching/damage and should be safely stored.
Other shapes also available on back order.