Grain Count The grains lines that are visible on the surface of the guitar top are the result of each year's annual growth and are often referred to as annual growth rings. Wood that exhibits tight close grain tells me that the tree grew at a very slow even rate with little variation in the growing season and climate. Master grade tops typically have very fine, close and evenly spaced grain lines.
Grain Visual Appearance – Suppliers will also grade their wood by the visual appearance of the grain and how consistent the grain lines are spaced apart. Even grain spacing is evidence that the tree grew in a very predictable and consistent manner. Grain coloration is also a factor to consider. Some tops have all the same color of grain lines; some have dark prominent grain lines while others have a mixture of light and dark grain lines within the same top.
Grain Straightness – Tops are also graded by how straight the grain lines run from the top to the bottom. Higher grade tops will have nearly perfectly straight lines which indicate the tree probably grew towards the middle of a forest stand and did not have to fight the wind or sun. Wavy grain is usually downgraded slightly from master grade. The waviness has no bearing on tone or structural integrity or stiffness.
Overall Color – The highest “visual” grade tops are the cleanest, purest, whitest of tops. Some tops have some naturally occurring coloration. This color is often a result of climatic changes and mineral deposits of the soil. Tops with some coloration are downgraded from master grade.
Degree of Cut – By looking at the end grain of the top you can quickly determine the accuracy of the mills quarter sawn or radial cut. The best processed tops have the end grain standing 90* perpendicular from the top’s face or surface. As the grains start to lean a few degrees off of perpendicular the top is downgraded proportionally from Master grade. Some of the very best tops are hand split from the log into billets. Then the billets are then hand split into wedges that are later milled into tops on a large band saw.
Run out – Is usually revealed by improper milling of the wood. Each tree has some degree of run out because of the twist that occurs naturally in a tree. Every log will have varying amounts of grain run out. Only the straightest logs are selected for musical grade wood. As the tree grows it constantly twists as it tries to follow the sun throughout the day. A tree is made up of billions of tube like cells that run from the roots of the tree to the leaves. Let’s compare a rectangular board to a rectangular box of plastic drinking straws. Looking at the open ends of a box of straws would be comparable to the end grain view of a top. These cells run the entire length of the top. Now if you looked at the top's surface in its longitudinal length you don’t see any [tube] ends or openings on the surface because each cell is laying parallel to the top's surface. Each of these tubes are oriented in the direction of the grain. As the straws are lying parallel to one another along the entire length of the box so are the cells in a top. This is how a top with no run would look like. If a top has run out then those cells or tubes would not be parallel to the top's surface but would be lying at a some diagonal angle. You would then begin to see the ends of the tubes show up on these surfaces.
Have you ever seen a guitar top that appeared to have one side that was slightly darker or lighter in color than the opposite side of the center joint? This is a perfect example of a top with run-out. The cell or tube ends that are not laying parallel to the surface have their cell ends exposed on the top surface. When these ends of the cells are exposed to the light they will refract the light at different angles and make the top halves appear to be different colors.
A very small amount of run out can be acceptable but a considerable amount of run out is not a desirable characteristic for a top. Run out is visually distracting. More importantly it causes structural weakness in the top rendering it considerable less stiff compared to a top with very little detectable run out. The highest grade tops are hand split so the face of the top always follows any run out that may exist in the billet. Much of the soundboard wood today is not hand split, because it is a very labor intensive process which in turn drives the cost too high. Instead tops are rapidly sawn from planks at the mill. Improper sawing will usually reveal varying degrees of run out in the top.
Medullar Rays or Silking – This is a visual sign that the top is of a high quality and was nearly perfectly quarter sawn. These rays or silking run at 90* to the grain lines on softwoods. Silking can be compared to re-bar used in concrete construction. This is the wood cells that lock or bond the longitudinal cells [or straws] together and they give the top extreme stiffness across the grain. Medullar Rays or Silking will only be visible in tops that have very little run out and were accurately quarter sawn.
Bear claw Figure – Is a naturally occurring figure that occasionally shows up in some spruces. The name was coined because the surface of the top appears as though a bear has left claw marks in the wood. No one knows for sure what causes this rare figure. The presence of bear claw used to downgrade the tops to B grade but in the last few years many luthier have discovered that these tops can be quite stiff and make strikingly beautiful and truly unique tops. With the recent swing towards the artsy look, bear claw tops are now even higher priced than master grade tops.