GlennYorkPA Posted January 24, 2009 Report Share Posted January 24, 2009 The recently issued Vol XXI No. 1 Journal of VSA Papers contains two interesting papers relating to the structure and composition of the ground asnd varnish of Cremonese instruments of the classical period. Having spent several hours attempting to understand just these two papers, and for the benefit of those who have not read them, I'd like to share what I extracted from them. Beginning with the second paper by Harris, Sheldon & Johnston -A Recreation of the Particulate Ground Varnish Layer Used on Many Violins Before 1750 - the authors end with some very useful definitions. Recognising that there is much confusion between the terms varnish, fillers, sealers, grounds and varnishes, the authors carefully point out that what they are referring to is a layer 35 microns thick (that's almost as thick as a sheet of paper), that does not penetrate the wood but lies on top of it and seals the open pores of the wood capillaries. To call it a filler or a sealer would be misleading because these substances are usually much thinner. As they say, 'a ground is the stuff one sees when the top varnish layer wears off an instrument made in the classical era'. The title of their article contains the word 'particulate' to recognise the fact that these classical grounds contain particles. This paper relates to the previous paper by Bruce Tai titled: Stradivari's Varnish: A Review of Scientific Findings -Part 1. This major review of all literature, historic and scientific, with 94 references, covers both ground and varnish of Stradivari's violins. Much of this review concerns the upper, colored, varnish layer. It appears that particles are abundant in most of the layers making up the complete wood finish and this makes it a little comfusing as does the fact that other makers apart from Stradivari are mentioned. There seems to be some agreement that it is the lower, ground layer that most contributes to the tonal properties of the instrument which is why Harris & Sheldon tried to recreate it. In a section subtitled: Further Considerations about the mineral ground, Tai notes that the most abundant particles to have been detected in Strad's ground are: Calcite, potassium feldspar, Gypsum and quartz. All are naturally occuring and of such a fine particle size that when dispersed in an organic matrix, the result is transparent. Apparently the particles are in the 0.5 - 2.0 microns. Now comes speculation on how these small sizes were obtained with the conclusion that 'how powders of such finenes were prepared in 17thC Italy deserves further investigation.......' Sooooooo, back to the Harris & Sheldon article, they formulate what they aptly call the 'Harris & Sheldon' emulsion ground varnish. It consists of an oil-resin mix, emulsified with glue and stabilized by clay-sized mineral particles (kaolin). They end up with a goop the consistemcy of mayonaise and apply it with the thumb. (Oh yes, epithelia/skin flakes are also found in Strad's ground indicating it was applied using the bare hand rather than a brush). Apparently the result of applying this to wood strongly resembles an Andrea Amati violin in Charles Beare's collection from which the top varnish has been removed. It has a low sheen and slightly chalky appearance. Glenn Quote Link to comment Share on other sites More sharing options...
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