This arises from two causes; either the varnish contains too much oil for the amount of gum and solvent used, or it is due to the varnish being applied to a surface not perfectly dry. To remedy this, allow the varnish to dry as perfectly as it will, so that it may sweat to the full extent. It is then rubbed down with a soft rag with or without fine pumice and a fresh coat of varnish applied. This trouble occurs mostly in the more durable exterior varnishes. "When the varnish shells off, it indicates that too little oil has been used in its manufacture, or that the varnish coat is exposed to excessive heat. When the varnish does not contain enough solvent, the resulting layer is too thick and the surface yields a skin, while the layers beneath remain viscous and it forms folds and wrinkles. This may also occur from a sudden change of temperature, or second coating before the first is dry.

The appearance of striae, or air holes indicates that too much dryers have been used, and it has not been allowed to age properly.

Pinholes may be caused by mixing varnish of different qualities.

Varnish spots or chills, when applied at too low a temperature.

Varnish will draw or pull if the surface on which it is put has not been properly prepared.

A greasy surface causes unequal coating and a tendency to separate or crawl.

When under the influence of too much heat, varnish blows or blisters.