On Monday, March 19, 2007 3:53 AM "Clive Titmuss & Susan Adams" <[EMAIL PROTECTED]> wrote:
> Thanks for the info, Richard. > > I was particularly interested to read: > > Turpentine never completely evaporates. A small percentage remains in the > varnish as an elastic resinous substance. I'm not sure that this is actually true. Modern brands of double rectified turpentine (genuine turpentine) that are used to dilute oil varnishes either before straining (of newly cooked varnish) or to increase their brushability would eventually evaporate completely. A drop of good quality genuine turpentine on a piece of paper leaves no visible sign and smell after it's evaporated. I would actually hate to use such turps in my oil varnishes if they remained in them as 'an elastic resinous substance'. Thank goodness oil varnishes are elastic enough as they are and this may well be why old recipes do not mention of adding any other dilutant but oil (if there was indeed such a need). Well, perhaps they would but genuine turpentine was not yet available back in the 16th - 18th centuries. > I noted in examining the photos that I have of mastic used as a ground for > guitar rosette inlay, that even though the samples were literally hundreds > of years old, the mastic had shrunk very little if any and no elements > were missing. This indicates to me that the mastic retains some > elasticity even though the wood moves. I'm actually in great doubt that the word 'mastic' in this particular context (i.e. going back to your earlier email, with references to descriptions of guitars in catalogues etc) has anything to do with mastic as _resin_ but rather something that _hardens to act as an adhesive and filling material_. At least on two Spanish guitars that I have recently restored (a truly remarkable guitar by Juan Pages 1803 and one of the six guitars, that are known to have survived, by F. Sanguino c. 1760s), patterns of MOP in their rosettes were set in what appears to be a mixture of glue and wooden filings (most probably of ebony in the Pages and rosewood in the Sanguino). In fact, in case with the Sanguino guitar, more than a third of MOP pieces together with dark-brown paste were merely 'washed off' by the moisture that has got onto the area of the rosette and further inside of the instrument some time in the past. So the sticky brownish 'substance' that have formed caused some noticeable signs of discoloration on the inside of the soundboard. The decorative inlays in other areas of soundboards (beneath the bridge, on the soundboard extension over the neck and, occasionally, next to the outside rim of the rosettes) on the Spanish late 18th - early 19th century guitars (by such makers as F. Sanguino, Juan and Josef Pages, Josef Benedid and some others) are always made of wood. The MOP inlays that are often incorporated in such inlays were most evidently put there after the whole of the ornament was already in place: the housing for one MOP piece that I had to replace on the Pages 1803 goes deeper than that for the ebony inlay surrounding it. The accuracy and precision with which these kind of inlays are executed are simply mind boggling! I probably spend hours by just looking at them ... they are really amazing. There is a belief that decorations of this kind were manufactured by separate trades, not makers of the guitars themselves. This may indeed be the case, simply stemming from the fact that some ornamental patterns are virtually identical (and executed with the same breath taking precision) on guitars of different makers. On Italian 17th century guitars black paste, instead of wood, is used to fill in the ornamental inlays in the soundboard, as well as to hold ivory / bone / MOP rhombi, squares, or triangles in patterns surrounding sound holes or along the soundboard edge. Occasionally ivory or bone filings are found integrated into the black paste, giving it some sparkly appearance. The quality of the paste (i.e. whether it shows cracks or shrinkage) differs from instrument to instrument. On one of the Italian guitars that I have restored (from the first half of the 17th century) the paste looked very 'homogenous', with hardly any defects and of very even consistency which is particularly noticeable in the thinnest veins of the ornament. Because I needed to replace some missing bits of the paste (in the ring of ivory rhombi around the sound hole that were imbedded into it ), I took a small sample and placed it in a few drops of water. Very quickly it broke into floating black particles (most evidently ebony) giving some light brown tint to the water - strong indication that the paste is based on glue as a binding substance. So again, no signs of non-water based ingredients here. On my own reproductions of 5-course guitars with Italian style ornaments I use fine ebony dust mixed with isinglass glue and I never had problems with it (such as cracks, shrinkage etc). The grooves in the soundboard, before putting in the paste, are sealed with diluted clear isinglass glue. I would never venture to use anything like shellac dilution in methylated spirit for this purpose. Besides this step may not even be necessary for the Pages style of the rosette, simply because the dark paste ring with MOP pieces embedded into it are, as a rule, separated from the neighbouring areas of the soundboard with several alternating concentric rings of wood. > I doubt whether acrylic modelling > paste or epoxy has this important property. Similarly one can see plenty > of shellac and oil varnish finishes centuries old that have not crazed or > cracked, while the various early synthetic finishes used on pianos have > not been so durable and frequently exhibit damage related to substrate > movement. > > The samples of dammar resin that I looked at the local art supply store > were hard and inelastic. I'm hoping that's one reason that the original > chios mastic will be superior. I found that chios mastic was used as a > varnish resin for painting before dammar resin (from Indonesia) was > adopted as a cheaper and more abundant alternative in the 19th century. I do like mastic a lot but only as an ingredient in my own made oil varnishes. It's becoming rather expensive though, considering that it has to be 'reduced' by heating to at least 50% of its initial weight before it is ready to be added to the oil. > It's one reason to stick with the "natural" solution. Wholeheartedly agree! Alexander www.vihueladamano.com To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
