Characteristics 103: Discoloration Defects

In Characteristics 103 you will learn to identify a variety of naturally occurring discoloration defects that can affect the correct grade of a piece of lumber. 

Syllabus

103: Pitch

Pitch is an accumulation of resinous material (the hydrocarbon secretion of coniferous trees).  For grading purposes, pitch is identified in three ways (light, medium and heavy).  The grade rules [Standard Grading Rules for Northeastern Lumber para. 728.0] describe these degrees as follows:

Light – light but evident presence of pitch

Medium – somewhat more evident presence of pitch than light

Heavy – very evident accumulation of pitch showing by its color and consistency

This board shows examples of each of these Pitch degrees within the same board.

103: Pitch Streak

Pitch Streak is a well-defined accumulation of the Pitch in the wood cells in a streak. They are described as follows, with equivalent areas being permissible areas. [Standard Grading Rules for Northeastern Lumber para. 730.0].

Very Small – 3/8” in width and 15” in length

Small – 1/12 the width and 1/6 the length of the surface

Medium – 1/6 the width and 1/3 the length of the surface

Large – not over 1/4 the width by 1/2 the length of the surface

Very Large – over 1/4 the width by 1/2 the length of the surface

103: Pith

Pith is the small soft core in the structural center of a log.

Very Small Pith – not over 1/8″ wide and occupies on fact not over 1/4 square inch (1/8″ wide by 2″ long or 1/6″ by 4″).

Small Pith – not over 3/4 square inch (1/4″ by 3″, 2/16″ by 4″, 1/8″ by 6″, or 1/16″ by 12″)

103: Seams

A seam is an area of ingrown bark.  It often is ingrown at a knot and sometimes independent of a knot. [General Definitions & Instructions for Grading Eastern White Pine Boards para. 828.0].

103: Blue Stain

Blue Stain, also known as Sap Stain, is a discoloration of the wood caused by sap-staining fungi and can range in color from light gray to blue, or dark blue to purple in severe cases.  The fungi need oxygen, warm temperatures, and wood moisture content above 20% to grow and survive. Sap Stain fungi do not destroy wood fiber therefore do not reduce the strength properties of wood.  However, the discoloration effect of the fungi on wood is considered a grade-reducing characteristic in the appearance grades of Eastern White Pine.

Light – slightly discolored wood

Medium – a pronounced difference in the coloring of the wood

Heavy – so pronounced as to obscure the grain of the wood

 

103: Brown Stain

Brown Stain, also known as Coffee Stain, is a non-fungal staining of the wood caused by chemicals already present in the wood.  High moisture content and high relative humidity are precursors to brown stain.  As extractives in the wood undergo enzymatic changes in high relative humidity and high temperature environments, a browning of the wood can occur, it is very similar to the browning of an apple after the inner flesh is exposed to oxygen.  Precursors to brown stain often develop in the log and will become more noticeable during air drying of the lumber; specifically, during hot, humid summer months and it may be exacerbated by unfavorable kiln drying schedules.  Brown stain can range from a very light brown to a chocolate color, and in some instances may even appear pink or reddish-brown.  It is prominent around knots and other areas that are difficult to dry, such as around stickers placed between the wood for drying, or any area that was deprived of adequate air flow and evaporation during drying.  

Light – slightly discolored wood

Medium – a pronounced difference in the coloring of the wood

Heavy – so pronounced as to obscure the grain of the wood

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