The big puzzle for piano restorers.

All wire makers after 1840 used numbering-systems that looked very much like our present day system. However, every maker had a different diameter for the same number.
Wire-number 16 could mean:
0,910 mm (Webster),
0,886 mm (Müller = Miller)
0,930 mm (Pöhlmann)
0,940 mm (Houghton)
0,96 mm (Firminy)

The indications we find in a 19^th century piano usually consist of numbers stamped or written on the pinblock or written on the long bridge, but the same wire number could differ two sizes or more depending on the brand of wire. We only know more or less which wire was used by the various pianomakers over the course of a period of some 100 years from about 1830 to 1930. Most pianomakers up to 1830, sometimes longer, used Berlin wire which can clearly be seen by the entirely different numbering system, which lies just outside the scope of this article, but I will be happy to answer requests.

Webster's wire was favorite for most makers until about 1845, and much longer for many English makers. Miller's wire was very much in demand from the mid 1840's to the mid 1860's. After 1867 most leading pianomakers used Pöhlmann's wire with the exception of the French pianomakers, but Webster's wire and Houghton's were in demand in England. We must, however, bear in mind that changes to a different brand of wire with different qualities and different steps between sizes required a lot of recalculating and reconstructing and was therefore not done overnight. For me the picture of which pianomaker used which wire, becomes even more diffuse during the first decades of the 20^th century. We all know the outcome with the firm of Röslau, producing practically all pianowire for the European market and also large quantities for other parts of the world.
It would be very helpful if the following lists would become much more complete with other brands and their gauge numbers and other useful data.

Number	Webster	Müller	Pöhlmann	Firminy	Houghton
7 8 9 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25 25.5 26	- - - - - 0.702 0.724 0.746 0.767 0.787 0.807 0.827 0.847 0.868 0.889 0.910 - 0.956 - 1.000 - 1.050 - 1.109 - 1.194 - 1.275 - 1.370 - 1.469 - 1.565 - 1.660	- - - - - 0.660 - 0.700 - 0.742 - 0.788 - 0.835 - 0.886 - 0.940 - 0.997 - 1.059 - 1.124 - 1.193 - 1.267 - 1.344 - 1.427 - - - -	- - - - - - - 0.750 0.770 0.800 0.820 0.850 0.870 0.890 0.910 0.930 0.960 0.990 1.010 1.030 1.060 1.090 1.120 1.160 1.190 1.230 - - - - - - - - - -	0.50 0.55 0.60 0.66 0.69 0.72 0.74 0.77 0.79 0.82 0.84 0.87 0.89 0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.12 1.16 1.20 1.24 1.28 1.32 1.36 1.40 1.45 1.49 1.53 1.57 1.61 1.66	- - - - - - - 0.750 0.770 0.800 0.820 0.850 0.870 0.890 0.920 0.940 0.970 0.980 1.000 1.020 1.030 1.050 1.070 1.100 1.120 1.150 - - - - - - - - - -

Providing wire numbers can be found on the instrument, it is usually possible to establish the brand of pianowire used, by calculating the string tensions assuming one type of pianowire, then look at the logic of the graph that comes out. It is precisely the huge difference between the various numbering systems that often set out one particular brand.
To measure a string tension I use a simplificated form derived from the Taylor formula:

F = 2514 x f² x l² x d²

F = tension in kg (gravity 9.81).
f = frequency in Herz.
l = speaking length in meters.
d = diameter in meters (!)

This formula is based on modern piano wire, average density 7,85.
These data are all hidden within the number: 2514.
For Pure Sound wire this number is : 2530. (average density: 7,90)
For Malcolm Rose's wire the number is : 2488. (average density: 7,769)

Wire available for restorations.

Late 18^th century to about 1820	Malcolm Rose wire type B or C.
1820 - 1840	Malcolm Rose wire type C or D.
1830 - 1890	Pure Sound wire
1890 - 1930	Pure Sound wire in some cases.
1890 - present day	Modern cast steel wire in most cases. Pure Sound wire to improve change-over areas.

1830 and 1840: Malcolm Rose-D or Pure Sound are a matter of taste.
1890 and 1930 several piano factories went on using their old short mensurations with lower tensions. Only Pure Sound wire will give satisfactory results here.
All modern pianos with change-over areas with unsatisfactory sound can be improved by using Pure Sound wire instead of modern cast-steel wire, using the same diameters. It will blend in well with standard modern wire.

One must take into account that the important qualities of piano wire not only lie in lower or higher breaking strengths. The elasticity of a wire effects the exactness with which the harmonics are formed. Wire with a higher elasticity will have a brighter sound, resulting from stronger and purer harmonics. All along the history of the piano its sound changed from a silvery and pure harpsichord-like character into a more and more ground-tone based sound. So much so, that in the last quarter of the 19^th century compensation systems were invented to compensate for the loss of harmonics. Examples are the Duplex-scale system and the Aliquot system. It was quite normal for early 19^th century pianos to build dampers for the whole compass. Leaving the top octaves of a piano unmuted, became customary later in the century and was also done as a compensation for the loss of harmonics.
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