The Pharmaceutical Journal
Vol 273 No 7328 p832
4 December 2004

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Chemistry: once far from a pure science more
More on the mysterious custom of bedecking trees with rags or shoes more
How the restoration of paintings has become an art in itself more

Chemistry: once far from a pure science

In an essay published in Science for 5 November, Ursula Klein, a science historian from Berlin, has reviewed the different habits of chemists in the 18th and 19th centuries, and the change in background which they adapted to their purposes.

She points out that chemistry as an academic discipline developed in medical faculties, academies, botanical gardens and museums in the late 17th century. Over the next century it grew to become an established part of the intellectual world of Europe. Chemists in the 18th century were professors, teachers, authors of learned books, members of academies and scholarly societies — and, incidentally, frequenters of coffee shops and salons. They differed from other savants in spending many hours experimenting in their laboratories.

Chemistry and pharmacy were connected as far back as medieval times. The old alchemists contrived the distillation vessels which found their way into the laboratories of the apothecaries. Distillations and solvent extractions were not invented by apothecaries but inherited from 15th century alchemists. Relevant books dated back to Paracelsian times.

Throughout the 18th century the chemist-apothecary was highly respected across Europe. Marggraf and Henckel became famous for the extraction of natural remedies, and it was usual for 18th century chemist-physicians to market their own chemical remedies. Some chemists studied mining and metallurgy, amassing stores of information about minerals and studying rock strata and mountains. The blowpipe became a valued analytical tool. Some chemists turned their attention to other arts and crafts, making dyes and porcelain. Other chemists joined the search for substitutes for previously imported commodities such as sugar, coffee, brandy and liqueurs.

Klein maintains that it was less their theoretical knowledge than their experimental and natural historical knowledge that equipped chemists for their widely varied occupations as technologists. Chemistry was never a pure science, but the establishment of experimental demonstrations of the laws of chemical affinity added much to our knowledge of the world, at first in the realm of inorganic substances. Later, studies of natural history led to important advances in organic methods.

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More on the mysterious custom of bedecking trees with rags or shoes

Since I mentioned the habit of hanging scraps of clothing on bushes overhanging springs or wells (PJ, 16 October, p578), I have come across some interesting sidelights on this practice in a newsletter dealing with plant lore. A correspondent reported a so-called “rag tree” by a roadside in County Waterford in Ireland. It appeared to be a hawthorn but was so covered with clothing rags of all descriptions, including a complete ancient jacket, that the foliage was almost invisible. Despite the tradition that there should be a well nearby to prompt a rag-hanging custom, none could be seen in the vicinity.

In the Celtic fringe, it is usual for rag trees and wells to go together. In Greece, Turkey and the east generally there is also a strong correlation. In Wiltshire and Wales “clooties” — not always of rags but also sometimes of sewn cloth ornaments — can be seen overhanging springs. The custom is there attributed mainly to the odd devotees of Pagan culture. Elsewhere there seems to be a widespread folk connection between hawthorn and holy wells.

The most startling revelation offered by correspondents comes from the state of Oregon in the US. Here there is a tradition of “shoe trees”. In some farming regions, isolated trees left among the wheat fields are decorated with old shoes thrown into their branches on the approach of spring. Apparently people of all ages participate in this strange aberration but no reason for it has been forthcoming. Moreover, the species of tree chosen is not evident. Certainly there is no apparent connection with any kind of well or spring when it comes to suspending shoes in trees.

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How the restoration of paintings has become an art in itself

There recently seems to have been a spate of articles dealing with the art of preservation and restoration. In Nature for 23 September David Erhardt, of the Smithsonian Institution, discusses the cleaning of paintings, something which, as he puts it, “is one of the most controversial activities that can be conducted in a museum”.

Much of the value, both aesthetic and monetary, of a painting lies in its appearance, which in turn depends on the condition of its surface. After storage, sometimes for centuries, dirt, yellowing varnishes and any later overpainting may need to be removed to return the painting to near its original state.

The problem faced in restoring a painting lies in removing accumulated dirt from its surface without disturbing or otherwise altering the original layer carrying the design. This can prove difficult. In the past reagents such as solvents, spirits, alkalis, acids and salts have been used in conjunction with simple mechanical scraping. Experience has shown how solvent mixtures can be highly successful in cleaning, as can enzymes such as proteases for proteins and lipases for oils. Laser treatments that vaporise the contaminant layer have also been employed.

In recent years gelled reagents have been introduced. These are based on polymer compounds that enable the operator to localise the cleaning area and avoid the difficulty experienced with rapidly volatile solvents. Gelled reagents, however, can present their own, more acute, problems. One is the difficulty of removing the viscous reagent completely, particularly if it has penetrated into minute cracks. However, it has been found that removal can be aided by adding a trace of weak acid (for example, 0.05M acetic acid). This converts the reagent into a free-flowing liquid that can be removed with a cotton swab.

Inorganic pigments are usually simple to deal with, since most are insoluble in standard cleaning solvents, but organic dyes and pigments or associated plasticisers may prove troublesome. Thus, the development and testing of new cleaning techniques and reagents remains a daunting task for the painting restorer.

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