The shelf life for unopened TotalBoat Gleam 2.0 varnish is at least 1-2 years, if not longer, if stored under proper conditions. This is consistent with most other 1-part varnishes. The useful shelf life of an opened can of Gleam 2.0 depends more on the condition that the container was sealed, and how much varnish is left in the can. This can vary from a few weeks, all the way up to a year. The condition of the can is also important, as a rusty can has less of a chance to form a good seal. Storing the product at the proper temperatures and humidity will promote the longest shelf life for the product. The storage directions are printed on the label.
Completely closing the lid on the can will also promote a longer shelf life. If the lid is not closed completely, the solvents in Gleam 2.0 can leave the can, shortening the shelf life drastically, as the drying agents in Gleam 2.0 will create a skin on the surface of the varnish. Storing Gleam 2.0 with less than half of a can of varnish left can also have a similar effect. When the varnish skins over, the can is not completely compromised, but it should be understood that it will be of a thicker consistency, it will absolutely require straining with a paint strainer before use, and after this, the shelf life will be greatly reduced.
There are some tricks that people have tried to extend the shelf life of varnishes. One simple way is to dispense varnish into a can that has less room for air. For example, if you start with a quart of varnish and you use half of it, pour the remainder into a brand new empty pint can. This will reduce the amount of air that comes in contact with the varnish, and the new can will form a good seal. Another method is to displace the air in the can using products such as Bloxygen. Bloxygen is a can of compressed argon, which is inert, and is designed to blow as much of the oxygenated air from the paint can prior to closing it. Without oxygen, the paint can not skin over on its own.