I bet they piled on the varnish, many coats, while blocking out (sanding with semi-hard backed x-fine paper) between coats. 8-10 coats sounds like a lot but when you consider the amount of sanding between coats that's involved the resultant mil thickness isn't that much. It does yield a finish with a lot of "depth". It remains my favorite way to finish walnut. (I just finished building a black walnut table for a client, 12 coats of varnish. She was ecstatic, and paid me more than what I asked for.) No separate pore filling, each successive coat of varnish fills more and more of the pores, and then a couple extra coats after that. For a more subtle luster, I work with glossy varnish (for its better UV protection) and then rub out the final coat to a very dull look. Then a coat of paste wax restores it to a soft elegant luster.
Pretty labor intensive, but the results are worth it - to me.
I've executed varnish finishes that had many coats as I described, and when finally rubbed out and waxed I was accused of creating oil finishes. Some of you may remember the multi-barrel 1899H takedown I built. That's how I did that stock. I'll bet there's more than one high grade gun stock out there purported to be a "London Oil Finish" which in fact is merely a very expertly varnished specimen.
