Banister Varnish / Stain?

If you don't mind it darkening a bit, then just give it a few (i.e. at least three) coats of a decent polyurethane clear varnish. If you want to keep it very light, then a coat of either blond de-waxed shellac or water based clear quick drying varnish as a sealer coat first.

My main stairs have mahogany - or rather I think it is - a dark red wood. The attic ones were added afterwards and are a much lighter wood which was painted. I didn't like this as you can see them both from some angles. I removed the paint and experimented with different stains and a coat of varnish which alters the colour of the stain. After about 6 attempts I got a match I'm happy with. Used Wicks Professional Exterior clear varnish, which I found worked best thinned about 50:50 and applied 6 coats with a rub down with very fine wet or dry used wet between coats. It looks good and has proved durable.

Just finished building a staircase. It has been stained in medium oak using Liberon stain and the treated with Danish oil for a finish. Much better than varnish IMO.

I built the staircase, my wife stained and oiled it. She has done an exceptional job.

Thanks everyone for the advice, much appreciated. Me thinks it would be wise to experiment on some spare spindles I have with the options posted.

Will endeavour to post back my final choice.

Colin