by Eric Meier
The typical smart-aleck response might be: “well, red oak is red, and white oak is white. . .”
Not so fast. There are all sorts of color variations seen in oak lumber, depending not only on the exact species of oak, but also from the growing conditions from tree to tree. From first glance, just going by color, (especially if the wood has a stain applied to it), it can be difficult to tell the two apart.
So, how do you tell the two apart, and why would you want to?
First I’ll cover a few quick ways to tell the two groups apart, and then I’ll describe the working properties and characteristics of each group. But before we start, let’s take a look at the two groups, and which oaks fall into which groups:
Red Oak Group |
White Oak Group |
|
Oregon White Oak (Q. garryana) |
While there is one specific wood species (Quercus alba) that is commonly considered the “White Oak,” and there is one specific species (Quercus rubra) that is considered the “Red Oak;” the truth of the matter is, when you buy oak lumber, oftentimes you will not actually be buying these two exact species, but most likely instead you’ll be buying one of the oaks contained within the two broad red and white groupings found in the table above. Basically, you’re buying characteristics found in an oak group, and not necessarily an exact species.
Now that we’ve got a general overview of the species involved, let’s take a look at different ways that will reliably enable you to tell the two groups of oak apart:
1. Look at the Endgrain
A quick and fairly reliable way to tell the two oaks apart is simply by looking at the endgrain. In order for this to work, the ends of the board can’t be painted, sealed, or rough-sawn. A freshly cut oak board should be easy to distinguish:
Red Oak (left), White Oak (right)
The pores found in the growth rings on red oak are very open and porous, and should be easily identifiable. White oak, however, has its pores plugged with tyloses, which help make white oak suitable for water-tight vessels, and give it increased resistance to rot and decay.
(Also notice in the picture above how closely spaced the growth rings are on the white oak on the right, while the red oak typically has its growth rings spaced farther apart; though ring spacing is not to be considered a reliable method of distinguishing between the two in and of itself.)
One related test regarding porosity is to take a short section of oak and try to blow air through the pores. If you are able to blow anything through it at all, it’s probably red oak. Take a look at this video, where a red oak dowel was used to blow bubbles in a glass of water:
One exception to this rule is Chestnut Oak, which is still considered to be in the white oak group, even though its pores are large and open like red oaks.
2. Look at the Rays
When looking at the face of the board, especially in the flat-sawn areas, you may notice little dark brown streaks running with the grain, sometimes referred to as rays.
White Oak (left), Red Oak (right)
Look closely at the picture above, (click on it to enlarge it if you have to), and note the length of the rays in both types of wood. Red oak will almost always have very short rays, usually between 1/8″ to 3/8″ long, rarely ever more than 1/2″ in length. (Pictured above on the right.)
White oak, on the other hand, will have much longer rays, reaching about 3/4″ long or longer. (Pictured above on the left.)
This method is probably the most reliable under normal circumstances, and is useful in situations where the wood is in a finished product where the endgrain is not exposed.
3. Use Sodium Nitrite
While this method is most likely out of the reach of most hobbyists (myself included), using a 10% solution of sodium nitrite on the oak heartwood is an easy and extremely reliable (foolproof) way of testing oak.
I haven’t tried this method personally, so I can’t comment on it firsthand, but sodium nitrite (NaNO2) is sprayed or brushed onto the wood and observed. If it’s red oak, there will only be a small color change, making the wood only slightly darker. But if it’s white oak, there will be a noticeable color change in as little as five minutes, (though it can take longer if the wood is dry, or if the temperature is low). The wood of white oak will eventually change to a dark green or purple, to almost black. (See picture below.)
White Oak (left), Red Oak (right)
Only the heartwood will bring about the color change, not the sapwood. (As can be seen in the picture above.)
Apparently sodium nitrite is available from chemical supply stores. You mix it with water at a 10% solution and then simply spray or brush it onto the wood. You can also add 20% ethylene glycol to the solution as an anti-freeze if the temperature is below freezing. In this case, a full color change won’t be evident for up to 24 hours.
(Sodium nitrite photo courtesy of Forest Products Laboratory.)
4. Look at the Leaves
This option is obviously only available if you have access to the leaves of the living tree. If the tree has just recently been felled, or if it is still standing, and you are contemplating the option to have the trunk milled into lumber, here’s a quick and reliable way to tell the two trees apart:
 White Oak (Quercus alba) |
 Red Oak (Quercus rubra) |
If you look closely at the two pictures above, you’ll notice that the leaves on White Oak generally have rounded lobes, while those of Red Oak are pointed; and for most of the species in each of the two groups, this general rule of thumb remains constant.
The Characteristics of Red Oak versus White Oak
As to the reasons why you’d want to be able to distinguish between the two, most of the answers have been explained above, but I’ll recap:
- White oak is much more resistant to rot, and is suitable for water-holding applications, boat-building, outdoor furniture, etc.
- Red oak should only be used for interior pieces such as cabinets, indoor furniture, etc.
- White oak tends to be more dense, while red oak is a bit lighter and has a more porous and open grain.
- White oak is usually slightly more expensive than red oak.
