If the varnish was full gloss there should not have been settlement. If the varnish was satin finish the fillers or extenders used to reduce the gloss may have settled.
The increase in viscosity was caused either by loss of solvent due to evaporation or reaction with oxygen causing polymerisation. If the former add some white spirit, if the latter (and this will be apparent as the varnish will also have particles of semi cured product) throw it away as it will not as good as fresh varnish in appearance terms.
Any can of varnish will give ageing problems if the level is less than 2/3 in my experience.
One trick we used to use when storing airdrying products in the laboratory where I worked was to turn the cans upside down (ensuring the lid was secure, this meant the void then above the liquid became saturated with solvent vapour which prevented oxidation & also eliminated any solvent loss from the can lid. Again this was only useful when the can was more than half full.
Alternatively as mentioned decant from a large can into smaller ones for storage.
White spirits vs. mineral spirits
On this side of the pond, what you call “white spirit” is unavailable to most hobbyists. At work, I buy “Stoddard’s solvent” from a specialty supplier which, I believe, is what you mean. Or are “white spirit” and what we call mineral spirits (odorless paint thinner) one in the same?
Please allow another query. Why would turpentine be a less desireable choice in this case?
Thank you, Cockney, for your unvarnished response.
The problem isn’t the turps…
…it’s that partially cured varnish won’t dissolve in turps or mineral spirits.
Storing the can upside down that is. Makes perfect sense.
The varnish was a satin product. I used only a small amount before resealing the can, carefully wiping the groove clean before pounding the lid on with a rubber mallet. But at least two years have gone by, so it’s life-span was pretty much gone as far as I am concerned.
What means ‘tip out’ ?
I turn all my cans upside down…
…or back to upright and give them a gentle spin every time I revisit the shelf.
Not just varnish but paints, adhesives, etc.
Does anyone know the shelf life of an unopened can of varnish? I have a few that are 3-4 yrs old.
I call it tipping out
when i gently drag the tip of the brush (or edge of the foam brush) across the varnished surface to eliminate runs.
PS: Hey String, ever read “Travels With Charlie” by John Steinbeck? I received it as a gift and just started it yesterday evening. There is a full-sized poodle (Charlie) as a traveling companion on a round-the-US road trip.
Turpentine or Turpentine Substitute ?
Turpentine comes from trees & can be very slow in evaporation. This means drying can be excessively long.
White Spirit is also known as Stoddard Solvent.
12 months maximum
Was the shelf life at the paint company I worked for & that is reasonable.
I guess I meant
pure gum spirits. At least that’s what’s printed on the can. I love the smell of it when mixed with artist’s oils (linseed). I can understand why a starving Van Gogh might have poisoned himself by eating it!
I suppose there would be occasions when retarded evaporation would be beneficial when applying varnish.
Having the drying time retarded can be an advantage where you want maximum flow in the film. A big disadvantage of course is the chance that dirt & dust will settle on the surface.