You can varnish them. Oil based varnish may change the colour of the oak more than waterbased though.
Alternatively, you can can use a wax oil.
https://www.wood-finishes-direct.com/product/osmo-polyx-oil?sid=1
Alternatively, you can can use a wax oil.
https://www.wood-finishes-direct.com/product/osmo-polyx-oil?sid=1