Antique Measuring Instruments & Scientific Tools

This collection covers a narrow and well-defined category: precision bench measuring instruments from the late 19th to early 20th century, made in Switzerland and Continental Europe, used in the optical, horological and laboratory workshops of the period. Each was built to measure to a tolerance the human eye cannot reach.

About this collectionWhat's currently held and who buys it

The current stock is three pieces, each from a different bench discipline: a Swiss spherometer (curvature measurement), a watchmaker's measuring microscope (dimensional inspection at the watchmaker's bench), and a brass coverslip micrometer (laboratory microscopy support). All three from the Thomas Guenther Collection.

The category sits between three collector communities: the Scientific Instrument Society, the National Association of Watch and Clock Collectors (NAWCC), and history-of-microscopy enthusiasts. Pieces that document this overlap — the spherometer (used in both optical and horological workshops) and the watchmaker's measuring microscope (built on the same principles as the toolmaker's microscope) — carry value across more than one specialist market.

If you are looking for sextants, theodolites, surveyor's levels, telescopes or general workshop calipers, those types are not currently in stock; they are sourced periodically and added when available.

Typology · SpherometersCurvature measurement in optical and horological work

A spherometer measures the radius of curvature of a surface. The principle is mechanically simple and impressive in its accuracy: three legs of equal length form a tripod that rests on the surface, while a finely threaded central spindle descends from the centre of the tripod until it touches the same plane. The height difference between the legs and the spindle, read off a calibrated arc, allows the curvature to be calculated.

The instrument is associated with two professional environments. In the optical workshop, the spherometer was used to verify lens curvature during grinding and polishing, both for telescope and microscope objectives and for spectacle lenses. In the horological workshop, it was used to measure the curvature of watch crystals, domed dials, balance staffs and jewel profiles.

The Swiss spherometer in this collection is steel rather than the more common brass — unusual, and reflecting the requirement for stiffness and dimensional stability in fine curvature measurement. It carries the "Jauge Patent" mark (jauge is French for "gauge"), the Swiss cross, patent number 28680, and a cross-registered Deutsches Reichspatent (D.R.P.) number 150061.

Typology · Watchmaker's MicroscopeDimensional inspection at the watchmaker's bench

A watchmaker's measuring microscope is a hybrid instrument: a small inspection microscope mounted above a calibrated sliding stage. The user brings a small workpiece (a wheel, a pinion, an escape-wheel tooth, a jewel hole) into the field of view, aligns it on a graticule or crosshair, and then advances the stage by a measured distance. That measured displacement gives the dimension of the feature being inspected.

The instrument is the direct precursor of the 20th-century toolmaker's microscope used in precision engineering. In the watchmaking workshop, it was used for the dimensional inspection of:

• Wheel teeth pitch and profile
• Pivot diameter and conicity
• Escapement components, including pallet stones and impulse faces
• Jewel hole size and roundness
• Balance components and small staffs

The example here has a brass optical head and a heavy cast iron base — cast iron chosen specifically for vibration damping at the bench. It is unsigned, which is normal for the category. The Continental European precision instrument trade of the late 19th century often supplied unsigned instruments to retailers and workshops; signed examples typically carry the retailer's mark rather than the workshop's. The unsigned status reduces specific attribution but does not reduce category authenticity.

Typology · Coverslip MicrometersA specialised microscopy accessory

The coverslip micrometer exists for a specific reason that is worth understanding before assessing one. Victorian and Edwardian high-magnification microscope objectives, particularly corrected achromatic and apochromatic objectives, were designed and calibrated for coverslips of a specific thickness (the standard was 0.17 mm, sometimes 0.18 mm). A coverslip too thick or too thin introduced spherical aberration, blurring the image and degrading the resolution that the maker had built the lens to deliver. To get the best out of a fine objective, the microscopist needed to verify the coverslip met the specified thickness before committing to a long observation.

The example in this collection is a small brass instrument with a four-footed base, a lever-operated jaw mechanism that grips the coverslip, and a 0–360° vitreous enamel dial that reads the result. Internally, the jaw movement is transmitted to the dial via a fine chain of links measuring 2.2 mm each — in effect a mechanical amplifier that turns a sub-millimetre jaw displacement into a large, easily-read needle deflection.

The piece is unsigned, typical for this category. Specialist microscope retailers in London, Paris, Vienna and Berlin sold coverslip micrometers under their own labels, often produced in small workshops that did not sign their work directly. Original glass over the enamel dial, intact dial face, working chain and complete jaw mechanism define a sound example.

MaterialsBrass, cast iron, steel, vitreous enamel

Three materials carry most of the visual and functional character of this collection.

• Brass. The dominant material in late 19th and early 20th century Continental scientific instruments. Machines cleanly, holds fine engraving, resists corrosion well, and develops an even, warm patina with age. The watchmaker's measuring microscope (optical head, stage components) and the coverslip micrometer (base, frame, jaw mechanism) are predominantly brass.
• Cast iron. Used where mass and vibration damping matter more than visual finish. The base of the watchmaker's measuring microscope is cast iron, providing the stability needed for accurate measurement at high magnification.
• Steel. The body material of the Swiss spherometer. Cast and machined steel offers the dimensional stability and rigidity required for fine curvature measurement, and accepts a darker patina that contrasts strongly with the engraved patent plaque.
• Vitreous enamel and glass. The 0–360° dial of the coverslip micrometer is white vitreous enamel under an original glass cover. Both are intact on the example here. Enamel dials of this period are fragile and irreplaceable; an original, undamaged dial is a significant condition factor.

Origin & Patent MarksSwitzerland, Germany and how to read the plaques

The late 19th and early 20th century centre of precision measuring instrument manufacture sat in the Swiss-German-Austrian industrial corridor. Switzerland produced specialist horological tooling for the Jura watchmaking valleys; Germany produced optical and laboratory instruments for the universities and scientific industries centred on Jena, Berlin and Munich; Austria produced laboratory and surveying equipment from Vienna. The three traditions overlapped, shared patents (D.R.P. registrations cover several Swiss-designed pieces), and supplied a Continental European market that prized accuracy, mechanical refinement and durability over decorative finish.

AuthenticationReading condition and originality

Condition language for this category is precise.

• Original surface. A mid-toned warm patina on brass, with small natural variations and gentle wear at handling points, is original and desirable. A bright, uniform, freshly-yellow brass surface usually indicates re-lacquering or polishing, which strips the collector premium. The same applies to steel: an even, dark-grey patina is original; a freshly polished or wire-brushed surface indicates restoration.
• Original mechanism. The threaded spindle on the spherometer, the lead screw of the measuring microscope's sliding stage, and the chain-and-jaw mechanism of the coverslip micrometer should all operate smoothly. Free, repeatable movement is a strong sign that the instrument is functionally complete. Stiff, gritty or seized mechanisms suggest deferred maintenance or internal damage.
• Original dial and glass. The coverslip micrometer's white vitreous enamel dial under its original glass cover is the most fragile element in this collection. Cracked enamel, missing dial paint or replaced glass would substantially reduce value. The example here has the dial and glass intact.
• Original engraving. Calibrated arc and stage scales should remain legible. Engraved patent plaques should retain crisp lettering. Light wear is expected; loss of legibility on a calibrated scale is a functional defect.
• Workshop wear. Honest wear from working use, including small dings on cast iron bases, surface scuffs on brass at contact points, and gentle wear on adjustment knobs, is consistent with bench use over a century.

Honest wear from working use is consistent with bench use over a century. It is a sign of authenticity, not a defect.

For the wider authentication framework across precision instruments, see the antique scientific instruments guide. The Scientific Instrument Society and the National Association of Watch and Clock Collectors maintain reference archives that are widely used in this niche.

ProvenanceThe Thomas Guenther Collection

Each piece in this collection comes from the Thomas Guenther Collection, a private holding of antique scientific and horological instruments assembled over time. Thomas Guenther continues the collecting tradition associated with the Egon Guenther Gallery, which is documented separately on the site. Collection-level provenance at this level is unusual on individually-priced pieces in the €200–€400 range, where most market stock is anonymous. For collectors, named-collection provenance provides a documentable chain back to a known holding, which supports both authenticity and resale.

For background on the Egon Guenther and Thomas Guenther collecting tradition, see the dedicated Egon Guenther Collection page, and the wider biographical context in the Egon Guenther story.

BuyingHow pieces are documented and sold

Each instrument is researched against the available patent record, the form vocabulary of late 19th century European precision instruments, and direct comparison to documented examples in published reference and auction archives. Where a piece can be attributed to a specific maker or patent, that attribution is given with its supporting evidence. Where a piece is unsigned, the unsigned status is acknowledged openly along with the contextual reasons (small workshop production, retailer-led labelling) that explain it. Condition is documented in detail and photographed at close range.

Private viewings are available in the Netherlands by appointment. Worldwide shipping is arranged on request, with packaging selected for the specific weight, fragility and dimension profile of each piece — cast iron bases pack differently from chain-mechanism instruments with enamel dials. For collectors building across the wider scientific and horological vertical, see the parent antique scientific instruments and watchmaking tools collection, the sister sub-silos for antique microscopes and horological antiques and watchmaking collectibles, and the rare antiques and curated collectibles collection for signed cabinet pieces.

FAQFrequently asked questions about antique measuring instruments