Conservation of Instruments - Part 2

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  Article taken from "Backsights" Magazine published by Surveyors Historical Society


by David St. John

The author came to the field of conservation by coincidence.  As a designer of optical instruments, standards became a lifeline to the success of any technical assignment.  With regard to the conservation of scientific instruments, the lack of a standard of practice was quickly recognized.  Research of related standards within the industry helped from guidelines for preserving instruments of our surveying history.  The details of a practical standard began to accumulate over a period of years.  As interest in surveying history continues to grow, so will the need for appropriate conservation.  There is an awareness that any standard must be an enabling tool for a conservator to implement methods in an easily understood, economical and convenient manner.

Any standard should relate to a number of professionals within the conservation field.  The document must facilitate communication.  The initial thought was to develop a document specifically for the restorer, to be prescriptive and satisfy the technical aspects of conservation at a practical level.  With time, a concern developed about individuals who might have important requirements other than the restorer and there would be difficulties relating to an isolated standard.


The document is presently related to experience with limited types of instruments used in the surveying profession.  While other types have been accepted for restoration, the standard is centered on the following:

             Surveyor's Compass                        Octants                                     Microscopes                                            

             Spirit Levels                                     Plane Table Alidades                Refracting Telescopes

             Transits                                            Goniometers                             Planimeters

             Theodolites                                       Tilting Levels                            Sextants

             Dumpy Levels                                   Inclinometers                            Wye Levels


Consider the following list of materials found in a limited group of instruments from a single profession.  Add the hundreds of instruments from all scientific endeavors and the list becomes extensive.  Preservation is a long term concept.  Conservators tend to specialize in a narrow field but gain intimate knowledge about materials and treatments.  A standard of practice could be a focal point for dissemination of important information on conservation techniques and current practice.

                    Bell Metals                                Cloth                                    Brass

                    Paper                                        Bronze                                  Spider Web

                    Copper                                     Leather                                  Pewter

                    Varnish                                      Lead                                     Optical Cements

                    Zinc                                           Lacquer                                Gold

                    Animal Glue                               Silver                                     Lubricants

                    Nickel Silver                              Ash                                       Aluminum

                    Lignum vitae                               Invar                                     Maple

                    Iron                                            Oak                                      Solder

                    Ebony                                         Tool Steel                             Mahogany

                    Optical Glass                               Ivory                                    Float Glass

                    Cherry                                        Diamond


Characteristics that differentiate one make from another are important from an historical perspective.  For the most part these details are easily captured for reference.  The collection of more intimate detail provides historical advantage and a sensitive exposure to the work of the maker throughout his life.

Studies which provide historical advantage essentially are never complete.  The details take years to accumulate but eventually a substantial fund of knowledge will exist for others to study.  The present characteristics being collected are:

                                                Spindle tapers used between 1800 and 1900

                                                Thread classification of different makers

                                                Spirit Vial configurations, glass type and condition

                                                Materials and alloys used

                                                Construction techniques of the various makers

                                                Lacquers and colors, condition and physical parameters

                                                Lubricants and related galvanic couple

                                                Knurls and chamfers related to each maker

                                                Compass needle configurations

                                                Optical properties of systems and elements

                                                Casting quality and designs of each maker

                                                Machined surfaces, finish, tool marks, feedlines, tell-tales

                                                Divided circle characteristics and distribution of errors

                                                Hand engravings and embellishments

                                                Innovative features for the period

                                                SPECIFIC STUDIES  

                                                Permeability of brushed lacquers

                                                Surface preparation and adhesion of lacquers

                                                Color reproduction and bleaching effects of solar radiation

                                                Color fastness with the chemical bleaching in micro-climates of display cases

                                                Fungus treatments on early glasses

                                                Sterilization techniques and substrate compatibility

                                                Artificial aging of new lacquers

                                                Corrosion treatments and vacuum impregnation of dielectric materials

                                                Lubricants for use in long term preservation

                                                Atmospheric pollution effects on artifacts

                                                Microbiological contribution to corrosion

                                                Resolving questions related to the principle of reversibility


The use of appropriate camera equipment and lighting provides an important record of the artifact, its details and condition before, during and after treatment.  The use of color and orthochromatic film captures intimate characteristics which define, in part, the intentions of the maker and his execution of thought.  Such information provides sensitive historical advantage.  Photography also serves the needs of training other conservators and provides for presentations both general and professional.  There is a story to tell about instrument conservation, its problems and solutions.  Photographic records have other benefits.  Aside from being part of a documentation report of an assignment, photographs provide a means for communicating to a broader audience through articles and technical papers for the general public and within the profession.


The author, having been trained as an instrument maker, has personal insight into the type of details which should be collected to fully characterize an instrument and provide data to gain understanding of the thoughts and abilities of the maker.

A systematic approach enables the conservator to retrieve sensitive information which often proves valuable in the determination of provenance.  Selected features help greatly to identify a maker and the period in which the instrument was fabricated.

In addition to securing information of historical advantage, an appropriate examination provides the necessary information on the stage of condition of the artifact.  Each restoration is in a sense a design task in reverse.  The author is interested in "functional restoration".  It is necessary to gather a significant fund of knowledge from a an artifact in order to plan an approach for bringing back an instrument to its original function and appearance without an improvement on the work of the maker.

The examination report provides a tool for communication with other professionals and enables the task of restoration to be defined in terms of difficulty and cost.  This helps in third party evaluations and estimates based on the contents of the report.  Once it is agreed to proceed, further documentation is required to explain the materials and methods used.  The end result is a document that provides explicit information about the instrument, its maker, and the actual restoration.  This fund of knowledge is then available for use by other interested parties in future generations.  Ultimately such information can be supplied through a networking system within the conservation community, with convenient access by everyone.




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