Shellac flakes have a finite shelf life unknown to most users. Even if Shellac flakes are stored in a cool, dark and dry place, but older than 2 years (thumb rule), it will not dissolve completely in alcohol overnight when compared to fresh stock. When applied, it will be sticky and slow drying. If used for French polishing, more than the usual amount of oil will be required for lubrication. If shellac is used after this date, make sure that it dissolves completely in the alcohol. If you see a thick gooey gelatinous mass at the bottom of the jar, its past its shelf life and should not be used. It is always a good idea to buy shellac flakes as and when required.
Once dissolved in alcohol, shellac does not last more than 6-9 months at the most. Store mixture in a cool dark and dry area of your workshop. The ideal temperature is between 65-70 degrees F.
Always dissolve shellac as and when needed.