Kevin, double hollow ground means more than just being ground on both sides. The blade is actually hollow ground twice with different diameter wheels. Here's an excerpt from an article published by Dovo, the German razor makers. It explains what I'm talking about.
PRINCIPLES OF STRAIGHT RAZOR GEOMETRY In the beginning straight razor blades were wedge shaped, the sides of the blade were straight lines, not concave (hollow). These blades shaved as perfect as the later hollow ground blades, if sharp, but had some disadvantages. First, they were heavy, compromising balance. Second, due to the wedge shape, the sides of the blade above the cutting edge instead of the edge itself, primarily touched the hone surface while honing. Third, after years of daily use, the regular honing caused rapid thickening of the edge width, thus making sharpening increasingly difficult and time consuming. Therefore, the next step was to clear the blade sides from the hone surface, in order to reduce weight, and to use the back as a guide for keeping the correct angle of the cutting edge, with which it forms one plane. This was done by grinding away metal between the cutting edge and the back with a wheel, resulting in a biconcave, hollow ground blade (at first without a ridge), combining an extremely thin blade with a very small cutting angle under 15 degrees. The disadvantage of this second step without a ridge was, that the ultra thin biconcave blades were unstable in the direction perpendicular to the plane of the blade. Therefore the third step was to create a ridge parallel to the cutting edge, dividing the blade in two parts: an upper part between back and ridge, and a lower part between ridge and cutting edge. The ridge is created by grinding the raw triangular basic form with successive different wheel diameters: the greater wheel for the part between ridge and back; the smaller wheel for the part between ridge and cutting edge.
The result consists of two hollow grind blade divisions separated by a thicker ridge, with hardly visible smooth transitions. The closer the ridge is to the back, the more the type goes from =BC to 1/1 hollow grind. The ridge presents stability and vibrations which add to cutting performance, which can be identified by transversely rubbing the thumb carefully over the edge, causing a ringing sound. The ridge is not that thick that it touches the hone, of course, and you can hardly see or feel it. The three parts (two concave parts separated by the ridge) are identified under a sharp light: the ridge diverges the light and is therefore identified as a linear shadow, parallel to the edge. The full hollow grind blades have the ridge at about a little below halfway between back and edge; lower grades of hollow ground just behind the edge, or somewhat further to the middle of the blade. A full (1/1) hollow ground blade keeps a very thin edge even after a lifetime of honing and stropping; a =BC ground blade edge rapidly thickens after years of honing, because of the proximity of the ridge to the edge.
Sarge
