On 14 Feb, 12:37, Stuart Noble
wrote:
Two part bleach works well on bare timber, and will also sort of work
where the existing finish is oil or wax based. Won't work at all on a
polyurethane finish though.
Caustic dipping will help kill the orange but, again, not on a
polyurethane finish. Part 1 of the above bleach is a strong alkali
anyway, but part 2 (peroxide) is what lightens the wood.

Thanks Stuart.

I've seen a fireplace I really like on Ebay but the owner isn't sure
if the finish it has is polyurethane (lacquer?) applied by the
manafacturer which is non-removable or if it is Varnish which would be
removable.
Is there any easy way of knowing which it is?