A follow up to this question, which established that the hardness of the wood is less important than how you protect the surface. Suppose I use a very easily dented wood, let's say Chestnut(Hardness 500), what options do I have to protect the surface from physical damage?
You have several options. A good reference is Bob Flexner's books where he compares all in terms of hardness (which is what you're looking for), reversibility, transparency, dent proofness, water resistance, etc. I actually don't own the book (I borrowed it from my local library several times), but from memory, here's the order of protectability:
- Oil-based finishes (e.g., tung oil, boiled linseed oil). Very low in hardness, moderate in water resistance, easy in reversibility.
- Lacquer. Moderate dent resistence, lowish in water resistance, easy reversibility. Reverses with lacquer thinner.
- Shellac. Same as above. Reverses easily with denatured alcohol.
- Water-based polyurethane. Better dent resistance than lacquer or shellac but harder to reverse. (It requires a chemical stripper, but it's doable). Good water resistance.
- Oil-based polyurethane. Less prone to wear than water-based poly and more water resistant. Like water-based, it too requires a chemical stripper to reverse it.
- Two part epoxy. This is what restaurants use on their tables. Really good wear and resistance but practically impossible to reverse (should you need to repair the wood beneath the finish).
Bob also gives a series of tests you can do to determine which sort of finish works for your particular project. To determine its scratch resistance, for example, you can buy art pencils (e.g., HB, 2B, 3B) and attempt to make tiny scratches in the finish. Also, to determine water resistance, (if I remember correctly), he suggests placing a drop of water on a finish then covering it with a mug for 24 hours.
Most finishes, even the "penetrating oil" ones, don't penetrate very deep (maybe 0.020", 0.5 mm). The soft fibers below the cured finish fail, leaving a dent. Having a thicker, hard surface will prevent denting. This could be achieved with a thick "bar top" type finish, or a matte or piece of glass over the center portion of the desk.
what options do I have to protect the surface from physical damage?
"Physical damage" is really too broad a category to answer simply. It needs to be broken down a little in order better define what protection certain finishes can provide.
With softer woods conventional finishes don't really protect from significant impacts, such as would leave a dent, but do provide resistance to bruising (from lighter impacts, usually less focused by a sharp corner or edge) as well as the marking that typically arises from general use, mainly scratches and scuffs.
The harder ones — shellac, varnish and lacquer — will greatly improve even a soft wood's resistance to light markings. But any significant impact is still transmitted to the soft wood underneath the hard surface layer, leading to a dent. All such harder finishes are somewhat brittle and they can crack with such an impact, and begin to flake off. Polyurethane varnishes are popular partly because they have some inherent flexibility (toughness, as distinct from hardness) allowing them to absorb impacts better without cracking.
The bartop type of finish as already mentioned in the answer by OSU55 are a step above this. These are pour-on finishes usually, resulting in a very thick coating being applied by conventional finishing standards even at their minimum thickness. That and the inherent strength of the material itself lead to an extremely tough and durable surface. However, the thickness and the high-gloss surface is not for every taste — critics say it makes the wood look "plasticy" or like it's encased in glass. And because of the application technique where you pour it on it leaves either a characteristic rounded edge where it has been allowed to drip over the edge, or a visible clear edge, neither of which suit many types of furniture.