A Brief History of Piano Insulators

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Firstly, what is a piano insulator? Well, today we’d probably be more familiar with the terms castor cup or coaster… the small bowl-shaped pieces of wood or plastic that sit under the piano’s legs preventing damage to the floor. But in Victorian times they were a far more elaborate object, and often considered to be an important part of the piano.

close-up photo of four basic piano insulators
Four Kidsgrove piano insulators from the 1860s. Photo: Ellis Willis & Beckett Auctioneers

The term “piano insulator” first started appearing in newspaper adverts around 1850. One such advertisement read (albeit somewhat clumsily by today’s standards) …

BARLOW’S PIANOFORTE INSULATORS – A new invention, important to those who value quality of tone; by which inferior and weak-tone instruments are surprisingly improved in tone, whilst to those of first-rate makers they are applied with great advantage, as they are the means of obtaining a perfect vibration, a delicious sweetness of tone, with such increased power and brilliancy as are truly admirable, which can never be obtained from a piano standing on a carpeted floor, the deadening effect of which cannot be successfully overcome without them. Price 6s. the set.
James Barlow, inventor and manufacturer, 14, King William Street, Mansion House.

The product advertised was a set of small circular press-moulded glass cups on which the piano would stand. Curiously, here the product’s key selling point was it improved the quality of the piano’s sound. This doesn’t really relate to the “piano insulator” moniker.

This term suggests that the piano’s sound is insulated from the floor, preventing it from travelling to adjoining rooms/properties. Does this really sit with the idea of improving the tone? In fact, these glass accessories enhance the transmission of vibrations through to the floor, and this would possibly enhance the piano’s sound.

photo of an elaborate  green piano isolator seen from the side and above
A typical late-Victorian piano insulator

The popularity of piano insulators increased rapidly throughout the latter part of the 19th century. So much so that some retailers would give away a set with each new piano sold. At the same time, the product’s design became increasingly more elaborate and decorative.

One English manufacturer (John Derbyshire and Co.) produced a range of insulators in the shape of animals’ feet. These are now highly sort after.

Pressed Glass

Pressed glass piano insulators were produced in many different colours. Green was probably the most popular, but amber, blue, yellow, and clear glass examples were quite common.

a composite image featuring ten different piano insulators
A selection of glass piano insulators. Photos: Christine Hudson

Pressed glass, sometimes called pattern glass, was developed in the United States around the 1820s. It was first patented by John P Bakewell. It simply involved taking a measure of molten glass and forcing it into a pre-heated metal mould using a lever/plunger mechanism.

Piano insulators seemed to be most popular in the UK and Germany. But in 1901 American John Brissel introduced a bronze and metal insulator with a rubber base. This design again claimed to both increase volume and tone whilst preventing the sound from penetrating the floor.

The piano insulator did have other advantages. It helped prevent damage to the floor, be it wooden or carpeted. It also stopped damp rising up the piano’s legs and damaging the instrument — a different type of insulation?

Collectors’ Items

Glass piano insulators with their intricate designs have become highly collectable over recent years — more amongst the glassware enthusiasts than the musical instrument fraternity.

Piano castor cups are still produced and widely used, primarily to protect floors and carpets. Most are either made of hardwood, brass, or plastic, often with a rubber base, but you can still get ones made of glass. Manufacturers, however, no longer claim that these items improve sound quality!

This article was prompted by an auction listing seen recently. Four Victorian piano insulators (photo above) designed by R.H. Thomas from the 1860s were being sold by Ellis Willis & Beckett Auctioneers, Sheffield, UK.

Acknowledgements: I am no great expert in this subject and would like to thank Lindsey who runs the Heart of Glass website for her help in preparing this piece. Do take a look at her article on “Piano Insulators” for a fascinating and far more detailed exploration of the subject. And also go to Christine Hudson’s website lustrousstone.co.uk to see more beautiful piano insulator designs.


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