Varnish will go over Danish oil though it does make the use of the Danish
oil somewhat redundant.
Is it necessary? First and most important consideration when contemplating a
finish is, does it provide the provide the protection needed for the piece.
Considering it is a changing table I'd say yes.
Special considerations. Oak is an open pored wood so, to get a smooth
surface finish I'd recommend a pore filler. One that dries clear. I'd also
recommend, considering that varnish doesn't have a solvent, a complete and
immediate cleaning of the gun immediately after spraying not to mention
spraying it in the absence of anything you don't want to get coated with
slow drying overspray and bounce back.
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