If you'll be working outdoors, beautiful brightwork is best achieved if you can begin applying varnish in the morning on a dry, clear day. Stay out of the wind and direct sunlight, which can cause varnish to wrinkle and dry unevenly. Also, time your application so a fresh coat of varnish has adequate time to skin over before dew sets in. Better yet, apply varnish indoors, with adequate ventilation.
Most importantly, pay special attention to the varnish manufacturer’s recommendations for temperature and humidity, because these factors can have the following effects on how quickly varnish dries.
Low temperatures can delay drying.
Low humidity leads to longer cure times.
High humidity can result in low gloss.
If a coat of gloss varnish dries with reduced gloss, the cause could be excess moisture in the air because dew settled or it rained before the varnished surface was completely tacked over. If this happens, allow the varnish to dry completely, scuff or sand, and apply a new coat of varnish.