Pitting, Pin-holing, Pocking and Blotching

¶ Pitting, Pin-holing, Pocking and Blotching of varnish. The causes of these defects are similar and each of these difficulties denote relative degrees of the same general trouble.

¶ Pin-holing is the condition of varnished surfaces which show disfiguring by innumerable small holes resembling pin-holes.

¶ Pitting is the same pin-hole effect but the holes are larger.

¶ Pocking or Blotching describes the same condition but the indentations are still larger, taking on the effect of large scars.

¶ The causes which are usually found in such cases as are called pitting, pinholing, etc., are these: The mixing of two or more varnishes of different kinds or different brands together; change in the air from dry to damp; spreading the varnish in rooms which are excessively hot or excessively cold; brushing varnish over varnish or color which has not become bone dry or which is sweaty; varnishing in a room with a floor which is very wet or cold; placing cold varnish on warm panels or warm varnish on cold panels; lack of proper ventilation and a uniform temperature of from 70 to 80 degrees.

¶ In the summer time a sudden drop of temperature may cause the pin-hole or pitting of varnish if the air in the room is quite damp. The excessive moisture in the hot air is condensed on the surface when the temperature drops suddenly. The drops of water on the surface prevent the varnish from taking hold and the pin-holes result. It is just like rain on the surface. If it occurs after the varnish is brushed on and before it sets, the same action takes place,the water sinks in and attaches to the surface while the varnish recedes from the water just as water and grease separate.

¶ When brushes are kept in oil and not made perfectly clean before loading them with varnish they may place enough oil on the surface to cause pin-holing. Varnish 1 brushes, for that reason, ought not to be kept in oil but in varnish, preferably in the special brush-keeper varnishes made for the purpose.

¶ The defect called blotching may be caused by thinning varnish with turpentine or benzine. It may result from the presence of turpentine or benzine in the varnish brush which has not been thoroughly cleaned. Varnish brushes kept in oil and not cleaned perfectly are a fruitful cause of blotching. Varnish is very particular about what it associates with. It takes only a little of some liquid of other kind to start trouble. And the strange part of it is that the varnish contains oil and turpentine usually, but incorporated under heat and in correct ways.

¶ Improper or careless filling of wood is largely responsible for pin-hole defects. And on close-grain woods where no filler is used a first coat of varnish which is too thick will cause pin-holes to appear. The thick varnish fails to penetrate into the wood cells. The first coat of varnish should be thinned with about 25% of pure turpentine, for first coat only.

Next Page: Sweating Varnish.