Restore that heirloom!

Marquetry or Parquetry done in Stone is called PIETRE DURE or PIETRA DURA.
This is a section of a tabletop done by the Opificio delle Pietre Dure in Florence(1633-1649)for Ferdinando II de Medici. It was designed by Jacopo Ligozzi and Bernandino Poccetti.
Materials used are; Agates, Jaspers, Lapis Lazuli and Chalcedonies on a background of Flanders Marble.

Veneering

It can be done either by hand ( Hand Veneering ) with warm animal glues, made from bones, fish, meat or hides (rabbit skin glue is generally considerate the best).
Or in a Press ( Press Veneering ) with either warm or cold glue.
The Press can be either Platten ( for flat work ) Caul ( for Shaped or Molded work ) or Vacuum ( for Any Shape work ).
 

Hand Veneering

Handveneering or the laying of veneer by hand is normally done with warm animal glue.
To this purpose the animal,- or hide-glue is warmed up to 75° Celsius or 165° Fahrenheit but the temperature should not rise above this as else the protein chains start to breakdown and a distinct loss of "tackiness" is noted especially when the glue is reheated.
The warming of the glue is done either in a Bain Marie type warming pan or gluepot this restricts the temperature to 100° Celsius or 212° Fahrenheit, as when water gets warmer than this, the energy is used to convert water into steam.
In a waterless gluepot no water is used and they are set so, that the temperature doesn't exceed 75° Celsius or 165° Fahrenheit, this allows the glue to retain a much greater "tackiness" especially, if the glue is warmed up more than once.
 
The warm glue is applied with a brush to the timber, if the timber is very porous or the veneer is not flat, than it is best to apply a layer of glue, which is very much thinned down, a day before. This penetrates the timber and seals it, so that the next application of glue doesn't sink into the timber thus improving the "tackiness".
 
The fresher the veneer is the easier it is to glue.
In an old veneer the fibers seem to "set" and the cellulose, which keeps the fibers in place, is less readily softened thus making it harder for the fibers to shift along one another and allowing the veneer to lay easily flat upon the timber.
 
If a veneer is not flat than this can be achieved by wetting the leaves with water, and pressing them overnight between two flat panels, add a little Oxalic Acid to this water, for light veneers or those containing iron.
 
The first leave is now moistened and laid flat on top of the glue and partially warmed with an electric Iron, set on woollen, the warm glue remelts from this and the glue penetrates the wood and veneer, with a Veneering Hammer , this is a bronze hammer with a very wide pein, the excess glue is squeezed out from between the veneer and the wood. The airpressure helps the veneer to stick to the wood, but should be kept moist as drying of the surface makes the top shrink and thus causes the veneer to curl up.
Now the process may be repeated with the area next to it, until the whole leaf lays nice and flat.
 
If the surface needs more than one leaf then the first one is to be glued slightly over the joint line and the second one is glued with the veneer protruding the same amount over the joint line (place where you want the join of the leaves to be ), on top of the first one.
Then they are the both cut at the same time, after which the joint is rewarmed and the excess veneer may be removed allowing one to lay the veneer flat again.