This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
The joiner tightens up a mortise joint by fixing the tenon already close home to its shoulders with one or two acutely edged wedges cut out of clean straight-grained wood, coated with white lead ground in linseed oil for external or with glue for internal work. These are inserted and driven in between the tenon and one or both sides of the mortise, which is trimmed slightly dovetail to better take the wedges, and they are found to stop the tenon drawing quite as well as the pins which they have almost superseded. Joiners' work, after being fitted and framed, ought to be left to season as long as possible before wedging up, to do which a dry period is desirable, and care is necessary lest in the operation of cramping and wedging the splitting faculty of the wedge, noticed under this head in the Carpenters' Section, is overlooked and too much strain allowed to risk the soundness of the joint. In housing stairs to strings the joints are usually secured with glued wedges, though some joiners prefer fastening them with nails instead of glue. Cased window frames, when not built in with the work, are fixed in position with single or pairs of wedges driven in at the side between the lining of the frame and jamb recess, and at the head between the frame head at the pulley stiles and the lintel.