Other Varnish Failures

¶ Skinning of Varnish. This term is used to describe that condition which results when the cork of a varnish can is not put in tightly or not at all. The top varnish in the can oxidizes, forming a tough skin. This exposure also permits the evaporation, of some of the volatile solvents of the varnish and is decidedly detrimental to the quality of the varnish. The storage of varnish should always aim to keep it corked tightly and to keep it in cans which are full. An air space at the top of the can permits skinning. Large cans which have been partly emptied should not be kept half full, or with any air space at the top. Pour the contents into smaller cans which will be filled by the varnish.

¶ Varnish Spotting. Flat and discolored spots on new varnish may appear due to cold blasts of air hitting the fresh varnish while drying, to the splashing of liquids like gasoline, benzine, etc., on to the wet varnish. Such accidents may cause the varnish constituents to separate and flat or discolored spots may result. Splashes of water or contact with a stream of humid air will cause the varnish to become cloudy in spots.

¶ Fire Cracks in Varnish. These are very fine, delicately woven cracks in the underside of the varnish or surface coats. The cause is the same as for cracking and crazing as described elsewhere in this chapter. One or two extra coats of rubbing varnish will often eliminate fire cracks.

¶ Discoloration of Shellac. Shellac which is kept in tin cans too long will turn black or greenish black, due to the action of the alcohol in the shellac on the metal. Shellac should be stored in glass or earthen vessels and in the dark and, of course, must be corked up tightly.

¶ Shellac which has discolored this way is a loss. Nothing can be done to restore its color.

¶ Varnish Fails to Flow. When varnish is permitted to get very cold it will not flow properly and should not be applied until it has been placed in a pail of hot water and warmed through to the temperature of the surface to be coated. When a can of varnish has been allowed to remain uncorked for some time, or when a little varnish is kept in a large can with much air space at the top it becomes thick and will not flow freely or evenly. It should be warmed, thinned with pure turpentine and strained. Allow it to stand a few days then before using.

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