The Dearborn Telescope, circa 1864, Adler Planetarium & Astronomy Museum
This paper was presented at the 1999 AIC Annual Meeting/St. Louis
Introduction:
However, as
we conducted our examination, We found areas that displayed what could be the tube’s
original surface. The then current surface of the tube was very dark and opaque and, being
in a somewhat darken display area, it was nearly impossible to ascertain that the tube was
in fact a beautiful walnut burl veneer. The
decision was made to see what had made it turn so dark, if the original coating was intact
and retrievable, and to preserve what had been the largest telescope in the world.
First,
let’s explore the history of the Telescope and its makers.
Three
instrument makers ---Alvan Clark and his sons George Bassett and Alvan Graham of
Cambridge, Mass---figured importantly in the great expansion of astronomical facilities
which occurred during the second half of the 19th century. Almost every
American observatory built during this period, and some observatories abroad, housed an
equatorial refracting telescope, and often the auxiliary apparatus as well, made by the
Clarks. Five times the Clarks made the objectives for the largest refracting telescopes in
the world; and the fifth of their efforts, their 40-inch lens at the modern University of
Chicago’s Yerkes Observatory, has never been surpassed. Their optical work, which was
recognized as unexcelled anywhere in the world, was the first significant American
contribution to astronomical instrument making.
Alvan Clark
was born in Ashfield, Mass. In 1804, the fifth of ten children. Little is known about his father other than he was
descended from a Mayflower passenger, Thomas Clark. Alvan
began his professional career in a wagon maker’s shop. It was during this time that
Alvan visited Hartford and had his first exposure to art. So inspired, he quit the shop to
study drawing and engraving. Soon, he
traveled the Connecticut Valley painting small portraits of people who were later involved
in astronomy and Clark instruments. It was during this time he met his future bride, Maria
Pease. They married in 1826 and lived
to celebrate their sixtieth wedding anniversary, an event noted by Science Magazine (Science, vol. 7 (1886) pp. 303-304).
He worked as both and engraver and artist until 1836 when he renounced engraving to earn his living by painting portraits. He kept his studio open until 1860, however, when the Alvan Clark & Sons telescope business appeared lucrative enough to support his family.
Alvan Clark became a telescope maker almost by accident. As interest in astronomy increased in 1844, spurred by the appearance of the great comet the previous year, Alvan’s son George Bassett Clark, then a student at Phillips Academy, followed Newton’s example and took a broken dinner bell and melted it down to make a reflecting telescope. Alvan watched his son’s experiment with growing enthusiasm and, like any father, could not refrain from giving him the “benefit” of his “maturer judgement”; he then promptly became involved with the construction of telescopes.
It was son
George who was directly responsible for the first telescope and the nucleus of the
company. We know little of him, perhaps
due to the fact of his constant devotion to the business.
His brother, Alvan Graham, was as deeply involved in the business as George. While George did mechanical work, Alvan Graham,
with an eye as keen as his fathers, figured and tested the object glasses. (Alvan
Clark and Sons; Artists in Optics; Deborah
Jean Warner. Smithsonian Press, 1968)
“Clark
really had a knack for working glass. He
would test a lens in his workshop, sight a star with it and throw it out of focus so he
could see where the defects were. Then he would put some optical rouge on his thumb and
actually feel where the error was, the tiny bump on the surface, and polish it away”
(Geoff Chester, Naval Observatory. Smithsonian Magazine, September, 1998 pp28).
On the night of January 31, 1862,
while testing the lens of the Dearborn Telescope, Alvan Graham discovered the faint
companion to Sirius. The German astronomer Bessel, years before
had predicted this companion from the wobbling motion of that brightest star in the sky. (Undated
exhibit text)
How the Telescope came to Chicago
Because the records of the Chicago Astronomical Society were destroyed in the Great Fire of 1871, the history of the telescopes coming to Chicago is based upon a report given by the Secretary of the Society, Mr. Thomas Hoyne, on March 16th, 1874 which in turn is based upon his memory.
The first
movement towards the creation of an Observatory in Chicago took place in December of 1862.
A gentleman named Mr. Forey came to Chicago with the
authority to sell a large telescope manufactured in New York by Mr. Fitz for $8,000.00.
In order to
create an interest in the creation of an Observatory in connection with the then University of Chicago, it was determined that
Mr. Forey give a lecture about astronomy at the University. It was quite successful, and a
call for subscriptions was made. From that, a committee was created to expand the
subscription drive with a view to the founding of an Astronomical Observatory Society in
Chicago. The drive was highly successful and
a sub-committee was formed to visit New York as soon as possible to purchase the
“Fitz Glass”
In the
meantime, a member of the Committee, Mr. Mixer, learned of a “…..great telescope
left upon the hands of Mr. Clarke by the University of Mississippi, in consequence of the
breaking out of the war of rebellion”.
Mr. Hoyne
left Chicago January 20th 1863 for New York with the intention of seeing Mr.
Fitz, but instead left New York immediately for Boston to see Alvan Clarke.
While
Chicago was making their plans, the Director of the Cambridge Observatory had plans of his
own to make Clark’s “Great Glass” the possession of his Observatory. But with the outbreak of the Civil War, finding
subscribers in Boston proved very difficult, and his plans were put on hold. Upon being tipped off that Chicago had
learned of Mr. Clark’s work, Cambridge moved to secure the instrument first. Mr. Clark had a prejudice that his greatest work
stay near his home in Cambridge. But when Mr.
Hoyne came willing to pay the first installment that day, Mr. Clarke Sr. was convinced by
his son that.. “ His interest…… was secured at once in favor of a city that
did not higgle about price or
terms…….”. The
then record 18-½ inch clear aperture lens was purchased for Chicago, along with a
contract to mount it for $18,100.00. With the
purchase secured, the next important step was to provide a site to receive the telescope
and establish an Observatory.
In the early
part of May, 1864, with the site secured and the tower and its revolving dome of 90 feet
in height erected, both Mr. Clark junior and senior, arrived in Chicago with the glass and
mountings. Alvan Clark Senior stayed nearly
one month to see his work completed, and then left the instrument in the hands of the new
Observatory.
(Excerpted from the report
given by Thomas Hoyne to the Society and the Board of Directors of the Dearborn
Observatory March 16th, 1874)
The University gave Alvan Clark Sr. and honorary degree in 1866.
(“Alvan Clark and Sons;
Artists in Optics”; Deborah Jean
Warner; Smithsonian Press 1968, page 23)
From 1862 to 1868, the 18-½ inch lens was the largest in the world. Housed at the original University of Chicago in Douglas Park, it was used from 1864 to 1886. When the University was hard hit financially after the Great Fire of 1871, and the resources of those supporting the Observatory were hit equally as hard, the endowed observatory found itself in severe financial difficulties for a period of several years. In 1881, the University became involved in legal action over its property. This ultimately lead to the Chicago Astronomical Society gaining possession of the telescope, and on July 14, 1887, the Society was serve notice to vacate University of Chicago property by October 1. The result was the choice of Northwestern University in Evanston to become the home of the Dearborn Telescope. It was transferred in 1889. In 1911, a modern type of mounting and metal tube was constructed. The original lens was removed from the wooden tube and reinstalled in the modern mounting where it continues in use for instruction and research today.
In 1929, the
Chicago Astronomical Society transferred ownership to Northwestern University and then
donated this original historic mounting and wooden tube to the Adler Planetarium, then
being built.
(Excerpted from a booklet published
by Northwestern University, “ The Dearborn Observatory Past and Present….” 1964; plus an undated exhibit text)
Conservation
Examination and Condition
Over the years, the wooden surface
of the veneered tube had apparently been routinely revarnished, perhaps as part of a
maintenance plan. This varnishing had
deteriorated over the years darkening and obscuring the wood. It is conceivable that the materials used
naturally darkened and the surface was resaturated with the same varnish to clarify the
surface accounting for the numerous layers found.
Fortunately, the metal elements
attached to the wooden tube had not been removed when the surface was recoated. This
allowed access to what was believed to be the original surface. Removing one of the brass elements, we were able
to conduct distinct analysis on the suspect coatings.
In order to determine that the
original surface was intact, we began a series of empirical solvent tests. These were designed to get a feel for what the
coating in question may be. The first test
was with ethanol. The surface did in fact
react quickly affirming we had a spirit varnish, as opposed to an oil based varnish. A spirit varnish could be made up of any number of
natural resins that readily dissolve in ethanol. The list is long and includes shellac,
rosin (colophony), sandarac, Manila Copal, and many others.
An oil based varnish is quite different.
The process in the 19thC for oil varnishes used fossil resins like Congo
Copal or amber, which were cooked in an oil, usually linseed, until the resin broke down
allowing the oil to serve as a vehicle for the resin.
Once dry, the film would undergo a drastic change. Through both
polymerization and oxidation, the film oil crosslinks and become impervious to simple
solvent testing. With spirit varnishes, on
the otherhand, the solvent simply dissolves the resin being used to allow it to be spread. As the solvent (usually ethanol) evaporates, the
resin remains behind as the protective film which can be redissolved in that solvent.
These simple tests rule out a much more complicated series of oil based coatings and
allowed us to proceed to the next step.
We then proceed to try and
determine which resin makes up the film. As mentioned, the ethanol suggests a wide variety
of resins. Moving to a different class of
solvent will narrow down the possibilities.
The next solvent used in our test
was acetone. The number of natural plant
resins that are fully soluablized in acetone is more limited. The heavily degraded top
layers were quickly soluablized with the acetone, where as the undercoating (possibly
original) was more resistant to the acetone. This
gave reason that there were two distinct materials making up the coating history.
The solvent test results, and an
educated guess in coating materials of the period, led us to believe that we were dealing
with the easily degradable turpenoid resin, colophony, as the darkened top layers. Our suspicions also suggested that the
undercoating might be shellac.
To verify those suspicions, we
moved to the microscope with a cross section. Under normal light (125X) we could see the
distinct layering of many years of recoating. Switching
to the ultraviolet, those distinct layer became more pronounced. The top layers fluoresced
the common whitish-green often associated with most plant resins. However, the plugged pores of the wood fluoresced
orange, strongly suggesting the original layer was shellac as shellac has the unique
ability to fluoresces orange under the UV.
Biological stains were also applied to the cross section. (include results from the other stains that proved negative for protein etc) Rhodeman –B showed a positive for oils suggesting that the top layers had an oil component. Research into 19thC practices, and the results of the solvent tests suggested we may have had a rosin based varnish leanly bound with oil allowing the acetone test to put the rosin into solution. The original mixture would not have been the traditional oil varnish recipe described above, but rosin dissolved in turpentine (turpentine was commonly used, but another solvent is possible) and an oil added perhaps as a plasticizer. (find a reference in the old text and include as a footnote).
In an effort to confirm our
suspicions of a colophony based varnish as a top layer, and shellac as the original, we
moved to Fourier Transfer Infrared Spectroscopy (FT-IR).
The FT-IR spectrographs were very
useful in ruling out a large number of natural plant resins and narrowed the focus to
colophony and shellac enough for us to make the determination and design the treatment. While the spectrographs suggested that both the
degraded over-layer and the degraded under-layer may have been the same materials, we
determined that we had possible resin mixtures along with the fact the materials were
somewhat degraded. Further analysis in the
form of gas chromatography mass-spectrometry (GC-Mass Spec) was deemed unnecessary.
Treatment
With all of the evidence from our
solvent tests, cross section staining, and UV fluorescence, and with enough verification
from the FT-IR to confirm rosin as the principle resin in the degraded upper layers, we
proceeded to devise a treatment. A wide
variety of materials were tested including aqueous based cleaning solutions, including
resin soaps (footnote abetic acid and other recipes).
While these water-based solutions cleaned the rosin surface well, they were not aggressive
enough to remove the degraded layers. Our initial solvent tests led us to begin with
acetone as a possible tool.
After numerous areas of bubbled
veneer were stabilized with hide glue (251 gram strength) and losses were filled with both
small patched of new walnut veneer and colored wax, the surface treatment began.
Free solvent acetone proved to be far too unwieldy and aggressive. Adding a small amount of mineral spirits (less than 10%) helps to slow the acetone’s aggressiveness down. However, working with a round tube, and the high volatility of the acetone/mineral spirits mixture, we found the need to gel the mixture for control. (include gelling recipe)
Initially we worked under normal
light checking the results by ultraviolet fluorescence. We could easily see the amount of
degraded material being removed (green auto-fluorescence) exposing the original shellac
layer (orange auto-fluorescence).
The photograph was taken under ultra-violet
light which easily shows the green fluorescence of the overcoats of varnish over the
orange fluorescence of the original shellac. The many smaller squares are the
initially cleaning patches.
It should be noted that shellac is
known to change its auto-fluorescence from orange to green when it is exposed to extended
periods of high ultraviolet light. While the mechanics of this phenonomen are still
unclear,(footnote: current research is being done that has reproduced the effect), we are confident
this did not happen in this case as the telescope would always be in a darkened
environment preventing the ultraviolet damage to the shellac film. Switching from normal light to check progress
under UV fluorescence proved to be awkward and did not allow for complete controllability
of the gelled acetone/mineral spirits mixture. By
changing to working under UV fluorescence exclusively, we were able to easily see the
progress of the solvent gel. Once the orange
fluoresce of the shellac appeared we would quickly clear the gel and proceed to the next
section. For a project with such a large
amount of acreage (22 feet), this approach speeded up the treatment dramatically. Areas approximately 12 inches by 10 inches proved
to be the maximum that could be effectively and efficiently controlled.
Once the degraded layers were
removed and the original shellac coating was exposed, we could see areas in which the
surface was quite lean along with several losses. The
shellac film itself was intact and not terribly degraded.
In an effort to prolong the life of the existing film (by reintroducing a
solvent phase) and to help clarify it, the surface was lightly cleaned with ethanol.
It was determined that the
existing shellac surface needed to be protected as well as creating a more visually
pleasing surface. The addition of another shellac layer would have been negated a main
purpose of the treatment, which was to preserve this 19th century layer of
shellac. A new layer would have become
intractable from the original making the future separation of one from the other
impossible. It was decided that B-72 would be the resin of choice due to its clarity and
stability, plus allowing the original layer of shellac to exhibit its ability to fluoresce
orange. The choice of solvent was also important. In
order to create a sufficient bond to the shellac and still allow the B-72 to be easily
removed in the future without putting the original shellac at risk, xylene was chosen.
Tests showed that a sufficient bond existed and its reversibility with xylene was very
good.
However, due to the curved nature
of the tube, the B-72 (15% solution in xylene) created disfiguring sags. Once set, the B-72 film was abraded, but in order
to create the desired burnished surface, the B-72 surface was rubbed with ethanol in a
traditional French polish technique utilizing a cotton pad wrapped in cotton sheeting. While not adding any additional resin material,
we were able to reduce the sagging and brush marks and create a very smooth surface by
manipulating the surface with the ethanol.
As part of the documentation, a
small (3X 3 inch) area of the degraded top layer was left intact near the lens end of the
tube.
We next turned our attention to
the brass mounts. Initial examination showed no coating on the brass except for a small
area on the base that tested for cellulose. Our
conclusions were that the brass, while it may have had a coating applied in the
1860’s, that been routinely polished removing all traces of any possible coating. The small area that tested for cellulose would not
have been original and very possibly applied at a later date. One small round crank that
was not attached to the telescope, but believed to be from it, was brought out of storage. This small crank did exhibit a coating that was
not analyzed, but could conceivably exhibit an original metal coating. This part was returned to the archive, as its
original location could not be determined. (note: since the telescope had been accessible
to the public for many years, numerous parts were missing).
Through years of handling by the
public, the brass elements exhibited a heavy layer of grime as well as a heavy layer of
oxidation. The decision was made to polish
the brass elements enough to remove the oxidation layer, but not to create an overly
polished surface. Precipitated chalk was tested and proved too slow for such a large
project due to the degree of oxidation and accumulated grime. Autosol (add detail footnote) was the next choice which proved very effective. Once the metal surfaces were cleaned, on both the
tube elements and the base, the surface was sealed with Agateen #27 1:1 to thinner.
The cast iron base had been
repainted in the past and the decision was made to simply clean the paint surface and wax
with a microcrystalline.
Another aspect to the project was
the four chamfered steel support arms. These
arms were attached to the wooden tube to prevent any distortion. The steel was covered with a pressed paper
material that was delaminating. B-72 (1:1
acetone/ethanol) was used to resecure the layers to the steel. The pressed material was not analyzed beyond
a cross section for microscopy. The cross section exhibited the same layering of
varnishes, but as the cleaning proceeded, it became clear that the original surface was
paint. A green layer was found which was thought to be the original. With the multiple
layers of added varnish were removed, the surface was found to be terribly abraded and the
decision was made to repaint these arms. An isolating barrier coat of B-72 (20% in xylene)
was applied and then they were painted with a latex in a similar green tone. (Note: it
was originally decided by museum staff that the arms should be black, and a black layer of
latex was applied only to be repainted with a green layer.)
I wish to acknowledge the
following people for their help in this project:
Christine Thomson for her
microscopy work.
Inge Feidler for her FT-IR
interpretations.
David Harvey for his
recommendations during the metal treatment.
Devon Pyle-Vowles, Collections
Manager for the Adler Planetarium.
Melissa McGrew for her endless
hours of work on the cleaning of the tube.
And Jennifer Yundt for her work in
the cleaning of the metals elements.