The Fossil Cleaner is a machine used to clean covered fossils. It is crafted by placing six aluminium plates on the top two rows of the crafting table, two redstone on the left and right of the bottom row, and a glass pane in the middle of the bottom row. When placed, it takes up one block of space.
You do not need to place the fossil cleaner next to a Fossil Machine in order for it to clean fossils. You will still need a fossil machine to extract the DNA of ancient Pokémon from the fossils that you have cleaned though.