Barrow Bells - Restoration Figures - Bell Weights, Size, and Pitch Harmonics

Introduction to the Figures

The restoration of the bells in 2013 discovered the fact that the weights stated in the Tower Log Book (1877) were not accurate.

The Whitechapel Bell Foundry weighed the bells after they had been cleaned, but before any other work was done to the bells. This revealed that the original figures under-estimated the weights of the small bells, and over estimated the weights of the large bells. The total weight of all the bells together was roughly the same.

Whitechapel Bell Foundry completed their work to the bells on Thursday 19th September 2013 (or thereabouts) and recorded some important information about the work they undertook to restore the bells. They recently sent the data to Nicholson Engineering (who have relayed this information to us).

Whitechapel completed 3 important tasks:

1. CLEAN - Remove the thick layer of corrosion from the bells (I believe they sandblast the verdigris)
2. CANNONS - Remove the loops at the top of the bell (known as the canons) used to strap the bell onto the wooden headstock. Nowadays bells are bolted directly through the bell into the metal headstock, with a resin pad between the two.
3. TUNE - a particularly skilful part of the restoration. The bell is spun in an inverted position on a large metal lathe, and shavings of the bell metal are taken from the inside of the bell to adjust the resonant frequencies of the different harmonics of the bell.

The following tables present all the data known for the bells using:

1. Details from Tower Log Book (1877)
2. Details from Whitechapel Bell Foundry - after cleaning but before any other work (2013)
3. Details from Whitechapel Bell Foundry - after cleaning, removal of canons and tuning (2013) = Current State of Bells.

BELL WEIGHTS

PRE-RESTORATION
Figures from Whitechapel Bell Foundry allow us to confirm or refute weights recorded in Tower Log Book in 1877
This next table compares weights from early tower records, against the actual weight of the bells measured after the corrosion was removed, but before cannons were removed and bells tuned.

The figures from the early tower records are noticeably different from the actual weights, with smaller bells heavier and the large bells lighter in reality than the early records.
However the total weight is only about 85kg different (3499Kg vs 3414Kg), and part of that total weight difference might be attributable to the weight removed when the bells were cleaned.
It would be easy to speculate that the original 1877 tower log figures must have been a 'estimates' based on the total bell metal used for the set of bells.

RESTORATION
Actual Figures Measured Before & After Restoration
This table compares the measured weight of each bell before and after restoration at Whitechapel Bell Foundry.
    BEFORE = accurate weight of the bell after verdigris removed, but before the cannons were removed.
    AFTER = accurate weight of the bells after all the work was complete (cleaned, canons removed, and tuned).

The removal of the cannons (a significant weight on their own) might have proportionally higher impact/change in weight for the smaller bells, but could simply be due to some bells needing to be tuned more than others.

BELL HARMONICS

How Successfully Have The Bells Tuned?

Nicholson Report about the tuning of the bells at Whitechapel Bell Foundry:

Whitechapel have been quietly developing a revolutionary new tuning technique for old bells over the last few years which they have used for a number of single bells. This is, however, the first time they have had a complete peal in for tuning in which all the bells were suited to this technique. The improvement is quite remarkable and has turned the bells into what will certainly be an exceptionally fine peal. I have been listening to and analysing the bells this morning and I am looking forward enormously to hearing them installed in the tower.

This method of tuning has removed some bell metal from the outside of the bell at the lip of the bell, in addition to the more typical removal of metal from inside the bell

Frequencies Measured Before & After Restoration
This table compares the measured frequencies of the harmonics of each bell before and after restoration at Whitechapel Bell Foundry. The nominal’s are relatively little changed. The dramatic improvements centre on the 2nd partials (prime/fundamentals) which have been improved out of all recognition, as have the hum notes which are the next in importance.

See the Strike Tone wikipedia article to explain some of these terms.

BELL SIZE

The tuning of the bells removed bell metal from the outside lip of the bells, and this has had an effect on the diameter of the bells

The table below compares the diameters of the bells before and after tuning