Friday, 21 March 2014

How to: cleaning rare books and special collections

On 13th March, I spent a lovely day at Clare College at a cleaning workshop led by conservator Caroline Bendix. It focused on the proper technique and tools needed to clean, dust and generally preserve any rare books and special collections within your library, but at a level that could be learnt by all members of staff, without needing trained conservators.

This was honestly one of my favourite training events of being a graduate trainee so far - Caroline was incredibly thorough but explained things simply and clearly, and brought a variety of brushes and damaged books for us to get some hands-on practice before returning to our own libraries.

Particularly since the Preservation Advisory Centre at the BL is closing, I was incredibly lucky to get the opportunity to attend this workshop (as they don't crop up very often!) and the more I learn about conservation, the more I wish there was a half-and-half post graduate degree that combined both conservation and library studies! Because I personally really enjoy the mixture of book history and acquiring practical skills, because I am quite good at brush-work and detail as I'm very artistic.

So I thought I'd share the report I wrote up after, in the hope that my notes might be of use to someone else! As all of our special collections need a clean now and again, but it's useful to know how to go about it in a safe and efficient way, not just barging in with a feather duster and causing havoc.
 Many thanks to Anne Hughes of Clare College for organising the day, and to Caroline Bendix. You can find her website here (it's worth a look!)

History of the book

 Caroline started off by explaining that there is a misapprehension that the value of a book lies solely in its contents, and gave a short history of the value of books as objects. I’d never thought of it like this before, but she pointed out that a book is actually a mechanical object with moving parts, and that conservation is about keeping it in working order (as you would for an any mechanism with moving parts) not just about preserving the text. The reason books are so easily damaged is because people don’t think of pages as ‘moving parts’ and don’t appreciate that there is only so much wear any mechanism can take – she emphasised that we should never open a book by more than 90 degrees for this reason, as you can still see the text perfectly at this angle.

After a quick hands-up quiz, Caroline explained that the first codex – the term for a number of plates sewn onto supports, whether papyrus, parchment, paper, or stone tablets – was actually first produced in 200 AD, although many people guessed around 1100 AD. It took over from the scroll format, and e-readers have only just begun to challenge the codex as the traditional vehicle for text, so as a format there is very little to be faulted.

 Book materials and structure

  •  Originally gatherings of pages were sewn together by hand. Caroline showed some of her own example bindings which used a variety of sewing techniques to stitch the text block together.

  • ‘Perfect’ binding was introduced in the 19th century but is ironically very flawed! Gatherings are glued directly onto the spine, which means the text block splits if opened more than 90 degrees. This is something to beware of when cleaning the inside of the book – use foam supports to ensure the spine is not put under stress. 
  •  Stitched bindings are much more flexible and can be opened at 180 degrees for 500+ years before beginning to show wear and tear. 
  •  Caroline next explained the different types of covers to look out for. Leather wears in three different stages, and looks three different colours as it wears down (original colour, lighter shade of same colour, then brown). When cleaning, we should pay attention to worn patches and use brush that isn’t too abrasive. 
  • Another type of hide binding material is ‘alum-tawed’ leather. This is cured with potassium and aluminium and bleaches the skin until it’s white and very soft, but is surprisingly actually more durable than leather. Tanning alters the chemical composition of the skin, and it gets weaker and more acidic once it becomes leather. However, you could theoretically ‘wash out’ the aluminium salts from alum-tawed, as it does not affect the chemical structure of the hide, so it decomposes much more slowly than leather. 
  • Book cloth was widely used as of the mid 1800’s, which was made of out woven calico or linen. 
  •  Marbling arrived in 17th century from Turkey.
  •  Engravings used to be hammered into leather by hand – each different piece of a pattern would be a separate stamp that was repeatedly chiselled on. This is either called gold tooling or blind tooling (if the engraving is just a dent not a colour) 

Dust in libraries 

Caroline is the advisor to the National Trust on library conservation in 150 properties, and has worked in numerous historic interiors that are open to the public. The next part of her training focused on dealing with dust in libraries, particularly focusing on historic collections. Over a 3 year period, she and other conservators took dust samples every 3 months in numerous National Trust libraries, and published their findings in 2002 and 2008 (I recommend reading the report - you can find it here).

After analysing the samples, their main discovery was that, unlike we’ve been led to believe, almost all dust is made up of detached clothing fibres. The minority of dust comes from binding materials, such as crumbling leather. The notion that dust is a result of dead skin cells is a complete myth. Amusingly, the majority of dust collected from properties in the Lake District consisted of denim fibres, while those in Chelsea consisted of cashmere!

Therefore, the greater amount of human activity in a library, the more dust, and dust is focused in the area around where people walk. There was a 50% reduction in dust deposition with every metre further from people. Also, very higher bookshelves tend to get less dusty than lower ones, since we tend to wear softer, more fluffy fabrics on our top halves, and the prime targets for airborne dust particles are therefore the shelves between waist height and head height. Dirt from the floor was found to only be kicked up about half a metre, so did not make a significant impact on books lower down, which was unexpected.

Dust becomes a real problem when the relative humidity reaches 65% - dirt binds more quickly to the surface of the book because calcite bonds can form in just a day in very damp conditions, and dust binds particularly well to organic materials – such as leather, cotton and silk – in this environment. This is because “humidity cycles cause physical movement of fibrous material that allow dust to embed deeper into porous surfaces”. If a room is very dry, the dust will sit on top for longer, rather than becoming ingrained or cemented to the underlying surface.

To measure dust deposits accurately, the conservation team left strips of twelve sticky samplers around different parts of each library, removing one sticky pad every 3 months, to be compared with samples removed before and after it, and with samples from different locations. These underwent computer image analysis to determine the percentage of dust deposition on the overall surface area. However, Caroline found that volunteers became worried about the amount of dust on the samples and the impression it would give to visitors, and felt the need to start cleaning when shelves looked “fairly dirty”, but when the surface coverage was actually only around 8%. They did not take into account the fact that different samples around the library would take different lengths of time to accumulate an 8% coverage of dust. For instance, if a sample was far away from thoroughfares, it could take up to three times longer to accumulate the same amount of dust as a sample close to a door. However, volunteers did not clean books on a case by case basis, and instead cleaned the entire collection, based solely on the results of the dirtiest sample.

 Caroline explained that unnecessary cleaning is ultimately more harmful to the books than leaving them with 2-3% dust deposition, as books have an abrasive element and are scraped between each other every time they’re used or cleaned. Therefore it’s important to make an objective assessment of dust on individual shelves before jumping to conclusions that all books are dirty. This does not necessarily have to be using sticky samplers or computer analysis of images, but a general rule is that if you leave a fingerprint mark in dust, it would benefit from a clean. Using your eyes alone is too subjective, as something might look dirty, but this dust could have been cemented to the text block long ago. Cleaning would be to no avail and you may actually damage the book by taking it off the shelf unnecessarily. In some cases, a problematic amount of dust takes 3+ years to accumulate, so Caroline recommended cleaning once every two to three years, maybe more in high humidity. In the case of National Trust libraries, Lloyd, Bendix et al. deemed that “as cleaning can cause damage through abrasion (and is resource intensive), it can be delayed until the dust has reached the identified levels at which aesthetic impact and public concern becomes significant” . This is especially true if your special collections are housed in a nice room, or shown off to a lot of visitors, rather than being kept under lock and key. Our rare books room is made mostly of metal and is very "80's" ... so appearance is not too much of a concern for us!

 Cleaning tools

Hog’s hair brushes should be used primarily for cleaning the outside of books, as they are quite abrasive. However, they shouldn’t be used if the binding is delicate or crumbling, as the hairs will easily pick up fragments of leather and speed up the  deterioration of the binding. In these cases, a softer brush, such as pony hair, should be used on the outside. A hog’s hair shaving brush (top left) should be used for cleaning away really thick, chunky dust.

Hogs hair brushes come in the widest variety of shapes, sizes and thicknesses. Caroline recommended purchasing a wide but flat hogs hair brush (top right) as a staple tool, as they are just the right shape for brushing down the edges of the text block. As a rule, these brushes should be used for cleaning off old dirt, not for cleaning little and often, as they are too abrasive if used too regularly.

Badger hair brushes are a similar thickness to hogs hair but slightly softer, more supple and less harsh on the book, but they are a lot more expensive. Hogs hair shaving brushes are often died to look like badger hair, but they are slightly different.

However, for the purpose of cleaning books, hogs hair brushes will suffice if used gently, and badger hair brushes are not an essential tool to have.

Goat’s hair brushes have much softer, fluffier bristles, but which are still quite wiry. They are good for brushing delicate items such as photographs or printed plates as they aren’t as likely to scratch as the coarser brushes. However, this does mean they are quite floppy and splay very easily so aren’t ideal for cleaning as they aren’t very precise. Caroline preferred using pony hair brushes over these.

Pony hair brushes have very soft bristles but keep their shape, so they give you a lot of control and precision when cleaning.

They are ideal for cleaning the pages and boards inside books, as well as damaged or brittle outer materials which could not tolerate abrasive brushes – for example, crumbling leather, weak joints, or tightly stretched vellum.

Caroline recommended buying at least one (if not two) of these as key pieces of your cleaning kit, as she usually reserves one for cleaning inside and one for outside books.

Squirrel hair brushes can be used for very, very delicate items, such as where there are tears in pages and bindings, insect or rodent damage, or very thin, delicate paper or material that is liable to break.

They tend to be flat brushes for the sake of precision and are incredibly soft to the touch (words can honestly not describe how soft these are!) but not an essential purchase because they’re only very necessary for damaged or excessively frail items. They are also very expensive!

Conservacs/Museum Vacs are small, often handheld, vacuum cleaners used for dusting artefacts, and can be used on books for more stubborn dust, and when dust is trapped in a difficult place (i.e. down a hollow spine). They cost around £250-300 and come with different nozzles, and are convenient because dust is sucked up into the machine and immediately out of the way, rather than brushed into the air where it can settle again. However, the brush attachment that comes with them as course is made with synthetic acrylic/nylon and isn’t suitable for dusting books because the fibres are far too abrasive and cause static electricity.

Synthetic brushes should ideally not be used for cleaning books. This is because the artificial fibres build up a static charge as you brush, which makes the dirt stick to the brush, instead of being removed from the book completely. You then continue to ‘clean’ the book with a brush that is covered in old dust. 

You might also have noticed that most of Caroline’s brushes have coloured electrical tape wrapped around the base of the fibres. This is for two reasons. The first is that the ferrule – the metal cylinder that secures the fibres to the handle – has sharp edges and can easily scratch or scuff leather and paper, so the tape covers these edges. The second reason is to colour-code the brushes according to where they should be used. If you’re not paying attention (and someone else is!) they can instantly tell if you’re using a brush which is too abrasive for the material you’re cleaning, and brushes used for the covers (that are likely to be dirtier) are not then used on clean pages. Caroline recommended that any and all brushes you acquire for the purpose of cleaning should likewise be covered in tape.

The colour code she used (although this is just an example) was:
Black = brushes to be used on the outside of a book
Yellow (or green striped) = brushes to be used inside the book
Red = brushes to be used only on mouldy books

Other rules she specified when cleaning books were:

  • Never wear cotton gloves! They’re too abrasive (you can see from the photo how much leather transfers onto the glove if the book has red rot or is fragile) and you lose manual dexterity.
  • Don’t wear hand cream. 
  • Don’t use ink pens. 
  • Remember that dripping noses are liquids too!! 
  • Golden rule when taking books off the shelf: don’t touch the spine. 
  • Don’t wear nail varnish (even clear) as it will inevitably chip onto books. 

 Method for cleaning books: 

Caroline stressed that a book must always be supported correctly when you are cleaning it - it should never be held in mid-air with one hand, nor should it be placed on the table as it will put the structure of the book under stress. She recommended using foam supports as the best way of doing this, rather than cushions. This is because cushions mean the weight of the book is resting on the spine (which is particularly bad if it's a hollow spine), whereas the foam rests mean the spine is in mid air. They also always support the book at 90 degrees, and can be stacked up to different heights/sizes so that they prop up the end boards with minimal human contact, if for instance you are cleaning the title page.

Always sweep dust and dirt into a dusting tray. Caroline made hers by scoring a piece of card to form a three-sided tray, and tying the edges with tape, so it can be stored flat.
  1. Start with the book closed and brush the top edge from the spine towards the fore-edge, using the very tips of the brush. Brush round the head band. This is where the majority of dirt will be, so it may be necessary to brush the top edge repeatedly, or use a smaller brush to get into corners. Then brush in one continuous motion down the fore-edge, always going in the same direction. Be careful of any untrimmed or disintegrating edges. 
  2. Repeat with tail edge and tail band. 
  3. Next clean the front cover. Start in the centre on the side closest to the spine, brushing outwards in a 'sun-rise' shape (see diagram). You must never clean the cover by brushing up and down in strips, or along the hinge and edges, as this is where the material is likely to be weakest, and brushing along an existing weakness will only make it worse.
  4. Repeat with back cover. 
  5. For the spine, brush from the centre of the spine towards first the head and then the tail of the book. If the spine has bands or raised supports, brush across the bands horizontally instead, as dust is likely to gather in these. Spines usually have the most damage out of any part of a book, so it is important to concentrate on this section, and to be gentle. If necessary, use a softer brush. 
  6. Inside the book, brush the joints from the centre outwards, as per the spine. Don't use an abrasive brush, particularly with glued bindings, as this is where the endpapers are weakest and are most prone to ripping, leaving the text block separated from the board. 
  7. Brush the inside board from the centre outwards, in the same 'sunrise' shape, using a soft fibred brush. Gently repeat this on every page until the title page, paying particular care and attention to the title page (and the edges of this page) as this is likely to be the most handled page of the book.
  8.  Repeat steps 6 and 7 with the back board and pages, until you meet the last page of text.

  9.  After covering the main areas, gently look through the book to look if there are any particularly dirty pages, and gently clean them with a soft brush. Do not be tempted to use a very abrasive brush on stains - dirt that is engrained will not lift away and you are likely to damage the paper more by scrubbing at it. It's all part of the provenance, and shows the book has been well loved! This is equally true of the top edge - lots of books will be brown on black on top, but scrubbing or sanding the pages to make them 'clean' again will actually do more damage than the dirt is. You must only ever lift away surface dirt, before it has bonded with the pages. 
  10. Look for any signs of insect or rodent damage - any holes made my pests will have sharply defined (and curved, if insect damage) edges. It may be necessary to brush away frass (woodworm excrement) from the pages, which is a fine sawdust-like powder. Use a very soft brush for this. 
  11. Last but not least, if the book is fragile or the boards are detached, tie two tapes around the volume, about an inch from the top and bottom (just one will put pressure on one end of the book and cause it to splay). Tie with a granny bow, not a reef bow - there is a difference! For a granny bow, you must (fight all your natural instincts!) and put the left hand lace behind the right before tying the bow, not over the right. This means the bow lies vertically not horizontally, so it is going in the same direction as the text block, and does not touch the endboards.

 Caroline ended the workshop with a phrase that really stuck with me - she said she "works on a 1000 year time frame", which I initially thought meant a really late retirement! But she explained that she looks both backward 500 years at past damage and stabilising existing weaknesses, and forward 500 years in order to prepare the book for future use, and so that any changes she makes can be easily undone when conservation technology and best practice has developed in centuries to come.

Both quotations and the diagram of dust deposition in libraries have been taken from Lloyd, Bendix, Brimblecombe and Thickett. ‘Dust in Historic Libraries’, 2008. It's available under a Creative Commons license from the National Trust's website, and is really worth a read before undertaking a cleaning project in any sort of rare books or special collections. It explains the science a lot better than I ever could!

Thank you for reading and I hope this was helpful!



  1. A very good summary of cleaning techniques. I went on one of Caroline's courses a few years back and purchased a Conservac for Catz

  2. One thing I took away from Caroline's course a few years back was the danger of mould spores. She said she could no longer eat Stilton cheese as a result of being senitized

  3. Thanks for this. I've had books damaged by mould and never knew what to do about it. This is very helpful'; I'll share it on my FB page: