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28 March 2023

Preserving Bach's manuscripts

Two Johann Sebastian Bach manuscripts in the British Library’s music collections, the autograph manuscript of the second book Das wohltemperierte Klavier (The Well-Tempered Clavier, BWV 870-893) and of the cantata ‘Wo soll ich fliehen hin?’ (BWV 5), recently received some much deserved attention from our colleagues in Conservation – and thanks to generous support from The Leche Trust. This blog post focuses on the work undertaken on the Well-Tempered Clavier manuscript, which we’re pleased to say is now complete.

Manuscript of the prelude in C major by J.S. Bach
Autograph manuscript of the Prelude in C major, from The Well-Tempered Clavier, Book II (BWV 870). Add MS 35021, f. 1.

The Well-Tempered Clavier, Book II

Bach’s Well-Tempered Clavier (named after a system of tuning – ‘well temperament’) is one of those musical works that seems to justify the grand claims made about it. On the face of it, it’s a simple series of preludes and fugues in every key, major and minor: 24 in all, with two sets of these (giving the series its nickname ‘the 48’)’. But it’s also a jaw-dropping feat of compositional virtuosity, with Bach using his immense contrapuntal skills to weave together separate musical lines that fit together logically (but never too predictably) and yet also produce inspired music at the same time.

The British Library’s manuscript of the second book of the Well-Tempered Clavier (Add MS 35021 and Add MS 38068) is really a set of individual manuscripts for 21 of the preludes and fugues in the second book (those in C-sharp minor, D major and F minor are unfortunately not preserved here and must have been separated from the others at an earlier date). These were composed between 1739 and 1742.

Each prelude and fugue was mostly written out to (very satisfyingly) fit on a single side of an open folded page, avoiding the need to turn the sheet over – even if this at times means a bit of a squeeze. (No amount of squeezing was going to fit the lengthy prelude and fugue in A-flat major onto one side – this carries on over to the next side). Most of the pieces have been written out by Johann Sebastian Bach himself, apart from four and a bit which are known to be in the hand of his second wife, Anna Magdalena (those in C minor, D minor, E major, G major and the beginning of the prelude in F major).


Manuscript of the prelude in C minor by J.S. Bach, in the hand of Anna Magdalena Bach
Manuscript of the Prelude in C minor (BWV 871), in the hand of Anna Magdalena Bach. Add MS 35021, f. 2

Planning – what were the issues?

Unfortunately, even in optimal storage conditions, chemical and physical processes that pose a risk to manuscripts like these can, over time, still occur. We minimise threats to the collection as much as possible, by controlling factors like temperature and humidity, by using appropriate housing and by limiting access to, and use of, particularly vulnerable materials. However, even with strict environmental monitoring a common problem that is difficult to halt entirely is one of iron gall ink corrosion. Like much music of this period and earlier, these Bach manuscripts are especially at risk from this due to the make-up of the inks that were used – iron sulphate and acidic tannins in particular, which, over time, oxidise and ‘eat away’ at the paper. There’s an interesting blog post on this on our Collection Care blog.

When it came to planning conservation work, there were two main issues to consider. One was the corroding ink, as mentioned above. This is a particular problem where the ink is applied thickly to a small area, as tends to happen when writing music notation. There were various examples of this on the Bach manuscript, ranging from visible holes to less obvious hairline cracks, making it extremely vulnerable.

Image showing the effects of iron gall ink corrosion on paper - there is a whole in the page
The effects of iron gall ink corrosion

The other issue was the previous method of preserving the manuscript. The manuscript pages were bound into a single large volume, with each folio mounted into paper windows. This mounting paper had aged poorly however, and you can see in the picture below how, over time, its acidic properties have led to it discolouring and becoming brittle – meaning some were no longer secure in the binding. Tension from the acidic border was also causing stress to the centre of each bifolio of the manuscript, increasing the risk of splitting. It was clear that the time had come to give the manuscript a more appropriate long-term home.

The old binding for Add MS 35021
The old binding for Add MS 35021
Image from inside the old binding, with the manuscript mounted in the old paper
Inside the old binding. Here you can see the manuscript in the old paper mounts.

Conservation over time

Something that really made an impression in the course of this project was the changing approach to conservation over the years – understandable given evolving knowledge, the emergence of new technologies and shifting emphasis in professional standards. So, while work undertaken decades ago might appear questionable now, nevertheless we can understand that it was done with the best intentions given the tools and knowledge available at the time.

A good example is in relation to iron gall ink. There are very few ways to fully halt the corrosive effects of the ink and limiting the damage is often the only approach. However, one treatment that emerged in the mid-1990s involves an aqueous treatment, using a Calcium Phytate solution to neutralise the acidic iron content in the ink.

In recent years, the British Library has established processes for this treatment. But still it is not something to be undertaken lightly. While extensive testing prior to treatment ensures that both the structure of the paper and the ink will remain secure, nonetheless the process has the effect of washing the paper, so removing dirt and accretions but also, potentially, valuable but less obvious evidence of historical use.  

The decisions are not easy, as weighed against the potential risk of sometimes losing potential sources of historical evidence, such as staining on the paper, is the risk of the manuscript deteriorating to such an extent that any kind of study becomes impossible.


Given the iconic status of this manuscript, many people were involved in decision making and the project was a collaboration between curatorial and conservation teams. One objective that was clear was that the folios of the manuscript needed a new form of housing, which would keep them more secure.

In terms of treatment of the iron gall ink, we decided to take a cautious approach for now, and only apply calcium phytate treatment to two folios, which suffered from different and more pressing issues from the others. These (which contained the A-flat major prelude and fugue, ff. 13 and 14), had been removed from the bound volume more than a century ago. At different points since then they had received conservation work of differing levels of invasiveness, including a coating of transparent heat set tissue applied to one side of the prelude and repairs along the fold of that page too. The aim in focusing a higher level of treatment on these particular folios was to remove the corrosive properties of the ink on one of the most problematic examples among the Well-Tempered Clavier manuscripts and also to reverse some of the ill effects of previous treatments. This work would also make it possible to more safely and securely house these folios in the same way as the other folios, removing them from their temporary housing.

Image of the Prelude in A-flat major (BWV 886), showing one leaf protected by heat-set tissue
Prelude in A-flat major (BWV 886), showing previous conservation work. Add MS 35021, f. 13v.

Conservation work begins

All our manuscripts are special and unique of course, and receive due care and attention to ensure their long-term preservation. But sometimes there are those manuscripts that are so iconic that to even look at them fills you with awe: in these cases the responsibility of ensuring their long-term safekeeping is immense. This was certainly the case here and it was a wonderful, humbling moment when the volume containing the manuscripts was unpacked in the conservation studio. We took a moment to listen to the pieces as we looked at the score - with the notes on the page almost dancing in front of us!

After thorough documentation and testing, treatment began by disbinding the volume and removing the folios from the acidic inlay paper; this was done mechanically using a poultice of sieved gelatine mousse. Whilst removing the old acidic paper mounts we uncovered the edge of the text previously covered by the inlay.

Aqueous treatment of the two folios

The treatment of folios 13 and 14 was achieved in three stages: first the documents were washed then treated with calcium phytate and then calcium bicarbonate. This helped stabilise the corrosive properties of the ink and remedy some of the ill effects of the previous treatment. 

Image showing conservation work under way - the manuscript is being lifted from the old paper mount in an aqueous solution
Removing the acidic paper inlay during aqueous treatment

Prior to immersion, multispectral images of these folios were also taken by our imaging scientist, ensuring we have a clear record of the manuscript prior to treatment. Multispectral imaging captures image data within determined wavelength ranges across the electromagnetic spectrum. It can be used to examine discolourations and staining, by comparing the "spectral fingerprint" of an accretion to a known chemical substance. It can also reveal things that are only visible on different parts of the spectrum and allow us to capture the true colours of the image to accurately assess any ink changes after treatment.

The existing condition of these particular folia made them a priority to treat in this way, but the experience of doing so will allow us to weigh in the balance the benefits or not of undertaking similar treatment on other folios in the future, should the degradation of the corrosive ink progress. For now, fragile inks on the other folios of the manuscript have been supported with a very fine toned Japanese tissue and gelatine using a low moisture technique. This was carried out over a light box to ensure any weakened areas of iron gall ink were spotted.

After Treatment

All the folios have now been housed individually in a more sympathetic, double sided mount. This rigid mount allows each page to be correctly supported and viewed in full and is suitable for both storage and exhibition display, minimising the need for handling or further work. These card mounts have then been stored in several specially made acid-free card boxes to offer protection on the shelf.

Image showing new card mounts for the manuscirpt
The new card mounts for each folio, with protective flaps at the front in back to keep the manuscripts safe in storage.
Image of one folio after treatment, in the new card mounts
Add MS 35021, f. 23r, after treatment, in the new card mount.


This work, undertaken thanks to the expertise of colleagues in Conservation and with generous support from The Leche Trust, has ensured that the manuscripts themselves are now better preserved and protected for posterity.

The British Library’s responsibility as custodian of these iconic examples of Bach’s creativity involves finding a balance between protecting the manuscripts themselves and finding ways for them to be appreciated by a wide audience. High-quality digital images are a key tool for providing access, but this conservation project will also make it possible for researchers to work with the original material where this is necessary – further enhancing our understanding of Bach’s creative practice. It will also make it safer to exhibit these iconic collections beyond the reading room, in our gallery spaces, where you can join us and experience the real thing.



Samantha Hare (Conservator)

Chris Scobie (Lead Curator, Music Manuscripts)


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