Using a stripper is less likely to result in sanding damage.

Sanding is not a good way to remove a finish.

The two best options for removing the finish are chemical or heat. Mechanical, which is what you've done, is definitely a third choice except for one attribute: it's accessible and controlable, even by a novice, and of course that's why you've chosen it. But it is labour-intensive and easily damages wood.

Chemical encompasses an enormous variety of options these days, which you can explore on this forum or on Old Houses by doing a search for "stripper" I would guess. Heat can be a heat gun ($75 or so, or you may already have one) or infrared, circa $500. The degree to which you affect adjacent surfaces may be a consideration with both chemical and heat - perhaps you can remove the window casing to avoid damaging it?

A final option is to not remove the old finish. But then you cannot stain, because stain needs to penetrate the wood. Instead, in this case you would have to paint something OVER the old finish - clear or otherwise.

Karin L

Thank you both for the information. Not sure which way I'll go, but I'll be doing either the stripper or the heat.

If it were me, I'd probably scrape off the vernish, then sand it smooth. Strippers are very hard to control in limited confines.
Casey

Casey's right - it is a perfect application for scraping.
The last time I suggested scraping it was pointed out that the finish might be too hard for a scraper, but the risk of damaging the casing with other methods makes that less of a concern.

Karin L