Re: Etymology of DADO
Don McConnell
>Dave asked:
"I�m curious how a cross grain groove in wood came to be known as a dado? Any theories?"
I have wondered if the "sunken" aspect of the architectural dado may not be related to the cross-grain dado, but find this unsatisfactory because it doesn't address the cross-grain aspect.
So, your question prompted me to delve into this a bit last evening. In the process, I ran across an entry for "Dado" in Peter Nicholson's _Encyclopedia of Architecture_ (circa 1850's) which *may* provide a speculative basis for a theory about this etymology. Following is the entry at length. This is easier than attempting to summarize or paraphrase, and provides some traditional woodworking content even if it proves entirely irrelevant to the question at hand. :-)
"DADO (an Italian word, signifying a die), a term for the die or plain face of a pedestal; that part of a room comprehended between the base and surbase. The dado employed in the interiors of buildings, is a continuous pedestal, with a plinth and base moulding, and a cornice or dado moulding surmounting the die. This continuous pedestal with its moulding is sometimes only made of stucco or plaster; but in well-finished rooms is constructed of wood, and is usually about the height of the back of a chair. Its present purpose, when employed, is to protect the stucco-work or paper of the walls, but originally it was used as an architectural decoration to the room.
"The dado is made of deal boards, glued edge to edge, the heading joints ploughed and tongued together, and the back keyed; the stuff generally employed for this purpose is whole deal; the keys are always made to taper in their breadth, and may be about three inches broad in the middle; they are let into the back of the dado by a transverse groove, which is either wider at the bottom than at the surface, or it is first made of a square section, which is again grooved on each side next to the bottom. Though the keys should shrink, those of this last form will always keep their inner surface close to the bottom of the grooves.
"Some workmen prefer the broad end of the key to be placed downwards; the lower end should rest firmly, either upon the ground or floor, and the dado should be left at liberty to slide downwards upon the keys. Others, again, prefer the wide end of the key to be placed upwards, and the dado to be fixed by this; the key, as it shrinks, will fall down from its own weight."
What strikes me is that the "transverse groove" across the back of the dado boards may well have been established with "dado" or double nickered "jack rabbet" planes. This groove could then have been modified to form a tapered sliding dovetail joint or "T-slot" (as I interpret the text). Possibly, the transverse grooves and the planes which produced them, came to have the term "dado" attached to them by association through their usage on the dado boards?
Needless to say, this is a conjectural theory, and I put it forth purely for its heuristic value.
Don McConnell
Eureka Springs, AR