Thanks all
Ben, I use epiphanes spar, best mail order price here, pricey shipping as it is volatile -
Flint Hire & Supply Ltd Epifanes Clear Gloss Varnish
This stuff has a very high tung oil content and is pretty thick. Decant a small amount into a small basin, set in a dish of hot water to warm up then thin up to 10% with white spirit before applying.
Best applied with a toothpick, bodkin or similar in
thin coats 24-48 hours apart. Work the varnish into the thread especially around the guide feet. Set guides down to help fill the tunnels (no turner needed) and wick away any excess after 15 minutes or so. You will need about 5 coats to just fill size A thread. Thread will usually go more or less transparent and darken considerably from spool colour, unless you use CP
After 4 coats set aside in a warm place for a week then razor or gently sand out any bumps or blips (1200 grit paper or fine fingernail buffer), then apply the final coat. Leave another week or three to fully cure the varnish before fishing. Varnish is pretty slow - but even slower if you glob it on.
Keep the tin well shut and sealed, keep it open for the shortest time possible. For guide wrap usage (a few mls per rod) it will go off long before you get through a 250ml tin. Also does for dip and wipe coats to (re)finish rods
Others say rustins and international schooner spar is OK too, but never tried them myself.