Collection Care blog

2014 marks the hundredth anniversary of another important event: the first use of ultra-violet radiation for the examination of manuscripts, and particularly the deciphering of palimpsests. Scholars are frequently challenged by manuscripts which have faded to the point of illegibility, or which have been deliberately erased, or, most challenging of all, which have been erased and then written over. The Archimedes Palimpsest is one of the most famous recent examples, but palimpsests have long been exercising the minds and eyes of scholars, certainly since the middle of the 19th century.

The Archimedes Palimpsest is a medieval parchment manuscript, now consisting of 174 parchment folios

Early attempts to make unreadable manuscripts readable, dating from the 18th century, used chemicals that would react with traces of iron in the fibres of the parchment which remained after the iron gall ink used to write the text had faded or had been removed. The trouble with these techniques was that, while they might initially be successful, they ended up staining the parchment blue or brown, leaving it even less legible than it was to begin with.

Photographic techniques had also been used to enhance faded writing almost since the invention of photography in 1839. In 1894 a process was developed for revealing palimpsests which used two plates: an over-exposed plate which would show both the upper and the lower writing, and an under-exposed plate that would show only the upper writing. A positive made from the under-exposed plate could then be used as a mask to permit an image of the lower writing only to be made. While this process was successful, it was time consuming because two plates had to be made, and their registration had to be very accurate in order for the upper writing to be cancelled out as nearly as possible.

In 1914, Father Raphael Kögel OSB published a paper in the Reports of the Royal Prussian Academy of Sciences in which he explained how ultra-violet radiation from an electric arc or a mercury vapour lamp could be used to excite fluorescence in parchment, but the fluorescence would be blocked (quenched) where the ink had originally been. A photograph of the visible fluorescence could then be taken, using filters to exclude the invisible ultra-violet which would obscure the image. This paper was in distinguished company: other authors in the same volume included Einstein and Planck. UV fluorescence photography should be distinguished from UV photography: in UV photography an image is made of the invisible ultra-violet radiation reflected from the manuscript; in UV fluorescence photography an image is made of the visible light emitted by the manuscript where it has been excited by ultra-violet radiation.

Father Kögel was born Gustav Alfred Kögel in Munich in 1882; he took the religious name of Brother Raphael when he joined the Benedictine abbey at Beuron, in the south of Baden-Württemburg, in 1898. He was sent to Brazil as a missionary, but fell ill and had to return to Germany. He then entered Wessobrunn Abbey, south-west of Munich, and was ordained priest in 1906. He later studied chemistry in Vienna, and in 1912 began working with the Palimpsest Institute at Beuron, which had been set up by Father Alban Dold specifically to study the Abbey’s rich collection of Carolingian and other medieval manuscripts. Here he developed his ultra-violet imaging techniques. He had previously experimented with coloured filters and photographic plates with different spectral sensitivities to improve the visibility of the under-writing, and also with chemical methods for enhancing faded writing, even though these had been condemned at the St Gallen conference on the conservation of manuscripts more than ten years before (“… this barbaric method …”).

Kögel became a professor at the University of Karlsruhe in 1921, and set up an Institute for Technical Photochemistry and Scientific Photography. Whether because of a crisis of faith, perhaps caused by the war, or simply because he found the academic life more congenial, Kögel left the church in 1922 and married in 1924. Kögel made important advances in using UV examination in forensics, and was also a pioneer in X-ray fluorescence analysis. His greatest commercial success was the development of the Ozalid diazo photocopying process, which was widely used until the 1970s. He died in 1945.

Because of the outbreak of war, Kögel’s publication does not seem to have been noticed in English-speaking countries until the early 1920s. For example, the first edition of C. A. Mitchell’s Documents and their scientific examination (1922) does not mention the use of UV, while the second edition (1935) does. Awareness of the technique grew in the 1920s and its use was well established by the 1930s. R.B. Haselden’s Scientific aids to the study of manuscripts, published by the Bibliographical Society in 1935, gives several examples of palimpsests that had been revealed by UV photography. He warns that users should wear protective goggles and protect their skin against excessive exposure to UV, and also that “prolonged exposure to UV light is injurious to a manuscript”. Unfortunately this message was not taken on board by everybody, and I have seen manuscripts where features that were seen and photographed under UV in the 1930s are no longer visible today. Haselden advises against the use of chemical reagents to restore faded ink, but goes on to recommend the use of a solution of anthracene in alcohol (“perfectly harmless”) to enhance faded writing – the solution penetrates the paper or parchment more rapidly where there is no ink, so the writing stands out against the vivid fluorescence of the anthracene under UV. Other writers recommend the use of a mixture of Vaseline and mineral oil for the same purpose, but it hardly need be said that these techniques are not recommended.

For best results, UV examination needs to be carried out in a darkened room, using a good-quality UV lamp and while wearing UV protection glasses. It has not always been thus. My wife remembers that when she was researching in a very well-known library in the 1970s, there was only one electric socket into which a UV lamp could be plugged, and this was underneath a table. She was therefore obliged to lie underneath the table with her manuscript and the UV lamp, sometimes with a member of the library staff to invigilate.

Folio 54 verso without UV illumination

Folio 54 verso with UV illumination

 The Electronic Beowulf project experimented with ultraviolet, first scanning fol. 54 verso under an ultraviolet lamp with a Kontron digital camera

UV examination is now being superseded in libraries such as the British Library which own multi-spectral imaging equipment. This gives better results as it can be much more selective than any process using filters to choose the wavelengths of fluorescence that are photographed. It uses much shorter exposures and therefore minimises the risks of exposing manuscripts to intense ultra-violet radiation. (See Christina Duffy’s blog post ‘Revealing hidden information using multispectral imaging’)

Dr Barry Knight, Head of Conservation Science & Research

References

Haselden, R.B., Scientific aids to the study of manuscripts, Supplement X to Transactions of the Bibliographical Society, 1935.

“Kögel, Gustav”, in Neue Deutsche Biographie 12 (1980) 295-6. www.deutsche-biographie.de/sfz43637.html

Kögel, P.R., Die Palimpsestphotographie, Sitzungsberichte der königlich Preussischen Akademie der Wissenschaften, 1914, 974-978

Mitchell, C.A., Documents and their scientific examination. London: C. Griffin & Co. (1922).

The British Library Science Team in collaboration with Festival of the Spoken Nerd put on a highly entertaining event last Monday night entitled I Chart the British Library. The event explored the highs and lows of data visualistion and was sold out attracting over 250 people to the British Library Conference Centre.

The show is part of a season of events at the British Library supporting the stunning exhibition Beautiful Science: Picturing Data, Inspiring Insight.

Hands up if you think science is cool!

The show was hosted by stand-up mathematician Matt Parker, geeky songstress Helen Arney and science experimentalist Steve Mould. The hosts were joined onstage by the British Library’s Head of Sound & Vision Richard Ranft who showed the audience some wonderful examples of how animal and bird sounds were historically recorded using musical notation – a lot different to how sounds are recorded today!

Collection Care was represented during the interval by a demonstration of the Library’s very own CSI team – Conservation Science Imaging of course! Audience members tested the contents of their wallets both under the microscope and under a multispectral camera to delve into anti-fraud techniques. The first thing we noticed was that some pound coins had the initials IRB under the Queen effigy, while others didn’t.

Analysing notes and coins during the interval

 

The £1 coin below on the left shows a portrait by Raphael Maklouf in which the Queen wears the George IV State Diadem. This design was in use between 1985 and 1997 after which a competition was held by the Royal Mint to design a new effigy. The winner was Ian Rank-Broadly and his design (right) shows the Queen wearing the ‘Girls of Great Britain and Ireland’ Tiara, with a signature-mark IRB below the portrait. To date three different obverses have been used.

Two one pound coins

IRB are the initials of the British sculptor Ian Rank-Broadly who has produced many designs for British coinage. The initials are difficult to make out with the naked eye but under the microscope they are clearly observable. Things to look out for in the case of counterfeit coins include date compared to design, edge lettering, quality, and orientation (the designs on both sides of the coin should be aligned when swivelled).

Close up of letters on a coin

“But what about hard cash?” asked one audience member producing a twenty euro note. "To the multispectral camera – poste-haste!" The design on the bank note is created using a variety of inks. Each ink has a unique spectral reflectance and so different parts of the design appear and disappear at different wavelengths as we move from ultraviolet (UV), through the visible (VIS) region and into the infrared (IR) part of the electromagnetic spectrum. Notes which don’t behave in this way are most likely counterfeit. Luckily no fakes were found!

A 20 euro bank note in different lighting wavelengths

Audience members were also invited to visualise sounds using spectrographs and to participate in a live analogue data collection and visualisation experiment conducted by Matt Parker.

Matt puts his volunteers through their paces in this live experiment

The goal was mapping back-to-back distributions of female vs male arm spans and a fantastic 137 people took part. The Libation Lab (or bar…) was also a huge hit and really made everyone appreciate all those sciency puns.

The night was a huge success and I think we all learned something new - well done to the BL Science Team! You can read more about their experience on the science blog.

Visit the Beautiful Science: Picturing Data, Inspiring Insight exhibition until 26 May 2014 in the Folio Society Gallery for free.

Christina Duffy

As an Imaging Scientist it is very difficult to look at ordinary objects without wondering what they would look like under a microscope. This was just the case when shown a beautiful printing block with a portrait of Steve Fairbairn, founder of the Head of the River Race, etched on the front. Printing blocks like these were used alongside similar-sized blocks containing type in a printing press to commercially produce images and text for publications. But how does it work?

The Fairbairn printing block, belonging to Pauline Churcher of Thames Rowing Club, consists of type metal (lead, tin and some antimony) with a copper electrolytic layer attached with steel screws to a 21 mm thick wooden block

The Fairbairn printing block, belonging to Pauline Churcher of Thames Rowing Club, consists of type metal (lead, tin and some antimony) with a copper electrolytic layer attached with steel screws to a 21 mm thick wooden block

The traditional printing method of letterpress is capable of printing solid colour from printing plates. In order to convey an image with varying shades and tones using a single colour, a reprographic technique called halftone is used. Halftone simulates continuous tone through the use of dots of various sizes, shape and spacing. The image is broken up into many small solid areas for printing. This gives the illusion of a continuous tone – but if we look up-close, we can see that the image is just an intricate pattern of dots.

Halftoning and halftoning close up: A series of dots of various sizes creates an optical illusion of continuous tone when viewed from a distance

This pattern is created using a printing block with tiny holes etched into a metal plate where ink can sit and be transferred onto paper. Below we see what the Fairbairn printing block looks like at 20x, 50x and 200x magnification.

The Fairbairn printing block at 20x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.

The Fairbairn printing block at 50x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.

The Fairbairn printing block at 200x magnification. These three images show the increasing magnification of halftone detail on the printing block (top 20x, centre 50x, bottom 200x). Ink is brushed over the plate and fills the hollows.

Before the inception of halftone printing, images were printed in books and periodicals using hand engraved metal plates or wood blocks. Wood engraving involves working an image or group of images into a block of wood for use as a printmaking and letterpress technique. Ink is applied to the face of the block and paper is pressed against it.

In ordinary engraving such as etching, a metal plate is used and is printed by the intaglio method where the ink fills the removed areas. When the excess ink is wiped away a sheet of paper is placed on top of the plate, and a blanket covers both to ensure even pressure when pressing. The paper is pushed onto the ink creating an image.

The idea of halftone printing is attributed to William Fox Talbot in the late 1850’s. There were many different methods to produce the halftoning effect, and the earliest trials involved directly etching the images formed on Daguerreotype metal plates. However, the time and skill required to perform such an etching, the inability to print images next to type, and the quick to wear out fragile plates, meant that the process was impractical for commercial publishing. The turning point came in 1881 when Frederic Ives patented a commercial halftone method in the United States.

Frederic Eugene Ives inserting a Kromogram into his Kromskop, circa 1899

 Frederic Eugene Ives 

Ives wanted to find a process to convert photographs into small black or white lines or dots, and to use a printing block which could be used alongside text blocks in an ordinary printing press. The lines and dots could vary in size, but had to be small enough that from a normal viewing distance they blended together giving the illusion of shades. 

The “Ives’ process” was gradually refined and photographs were rephotographed directly onto a metal plate coated with photoresist (a light sensitive material). The popularity of the process spread quickly and by the 1890’s it was used widely replacing earlier hand-engraved wood block and steel plate illustrations. This was the standard process for photographically illustrating books for the next eighty years.

A 3D rendering and colour scale display of the Fairbairn printing block shows that the depth of the stippling is about 86 microns.

3D visualiation of the halftone printing block. The dots are typically 86 microns in depth

Electrolytic copper layer

Type metal (or hot metal) is the metal alloy used in typefounding and hot metal typesetting. It consists of mostly lead with some tin and antimony. The type metal in this block has a copper electrolytic layer and is screwed onto a wooden block. The electrolytic layer is very thin and can be scratched easily revealing the type metal underneath.

Electrolytic layer scratches at 100x magnification

Image of losses of electrolytic layer at 200x magnification

 The copper electrolytic layer is easily scratched. Areas of damage where the copper electrolytic layer has been lost reveal the type metal (lead with some tin and antimony) underneath

The printing block is backed with a paper sheet and ink stains pervade both the backing sheet and the wood block giving a wonderful insight into the history of the item. We often forget that collectibles which today gather dust were heavily used at some point in their lives.

Profile of the printing block under the microscope lens showing printer’s ink residue and paper backing under magnification

Image taken of the profile of the block at 50x magnification

Halftones are considered to be what is known as a photomechanical or process print. Other photomechanical prints include line blocks, photogravures, photolithographs and collotypes. Digital halftoning replaced photographic halftoning in the 1970’s and the theory forms the basis for how the CMYK colour space works using dots of cyan, magenta, yellow and black. You can read more about CMYK in a previous @BL_CollCare post: What the CMYK? Colour spaces and printing.

The printing block in this article depicts Steve Fairbairn (1862-1938) and was kindly loaned by Pauline Churcher of Thames Rowing Club. The Head of the River Race is a 6.8 km processional rowing race held on the Thames each year from Chiswick to Putney with the tide. It was founded in 1926 by Steve Fairbairn who dedicated his life to the sport by both competing and coaching to high levels. The race began with 23 entries and today boats well over 400 crews. The coveted prize is a bronze cast bust of Steve Fairbairn - which is the image observed in the printing block.

Christina Duffy (@DuffyChristina), Imaging Scientist

Did you know that image resolution has absolutely nothing to do with how an image looks on a screen? It is a fairly safe bet that more of our collections will be digitised in the next few years. As technology moves on with great pace there is often debate as to the “best resolution” that images should be captured at. But what does that actually mean? This post will try to explain what is meant by the terms pixel and image resolution, and will demonstrate the relationship between them.

Pixels and megapixels

Digital images are made up of thousands or even millions of pixels (picture elements). A pixel is the smallest addressable element in a display device with a specific assigned value that can be read by a computer and mapped onto a grid to recreate an image. Each pixel is a sample of an original image, so the more samples available result in a more accurate representation of the original. We can change the appearance of an image by manipulating the pixels or by getting rid of some of them to reduce the file size. Below we see a digital image of the Gospel of St John from the Lindisfarne Gospels (British Library, Cotton MS Nero D.IV). It is obvious that the image with more pixels is of a higher quality than that with less pixels.

Figure 1: Cropped portrait of St John wearing purple, gold and green robes. 

Figure 2: Pixelated close-up image of the portrait of St John. 

Figure 1 has more pixels and so produces a more accurate representation of the subject matter. Figure 2 looks “pixelated” due to the visibility of the pixel boundaries.

How pixels control resolution

Pixels control image resolution because the closer the pixels are placed (i.e. the more there are per inch), then the denser the image becomes with detail. Similarly, the fewer pixels an image has per inch, the further apart they are spaced, resulting in less detail and an image of poor quality.

Image resolution is therefore concerned with the number of pixels per inch (ppi) printed out on a piece of paper, and the size of those pixels. Since the software takes care of the pixel size, it’s really just the ppi that you need to think about.

Let’s try to understand that better by taking a look at an image captured with a DSLR camera. Below is a photograph of our new multispectral imaging system opened in the open source image processing software package ImageJ.

Figure 3: Full-size, uncompressed photograph opened in image processing software package ImageJ.

If we look at the title bar of the image we can see some details about the image file.

Figure 4: The title bar tells us the name of the image file, the percentage size in brackets, and the number of pixels.

The title bar (DSC_0074.JPG (16.7%)) tells us that this file is only opening up to 16.7% of full size. The image is just too large to open on the screen at 100%. Below the title bar we can also see that the size of the image is 6,000 x 4,000 pixels (i.e. there are 6,000 pixels running along the image from left to right and 4,000 pixels running from top to bottom). That sounds like a lot of pixels. If we now zoom in on any part of the image we can see these pixels as little squares of colour.

Figure 5: A cropped portion of the original photograph.

Figure 6: Zoomed in portion of the original image. 

Figure 7: At maximum zoom it becomes apparent that the image is made up of pixels.

If there are 6,000 pixels along the top of the image, and 4,000 pixels along the side, then my incredible math skills suggest that there must be 24,000,000 (= 4,000 x 6,000) pixels in total, or 24 million pixels, or 24 megapixels (MP). A quick glance at the camera manual will show that this camera (Nikon D5200) has in fact got a 24 MP CMOS sensor, so our powers of deduction are correct.

Resolution doesn’t mean anything until you go to print

We now know that there are 6,000 x 4,000 pixels in our image. Great! But what does that mean if we want to print out this image on a piece of paper? How does a pixel correlate to the size of the page? Will the image fill the whole page or will it just appear as a tiny thumbnail? Take a look at the image resolution by opening the image up in another great open source image processing package called GIMP, and opening the Set Image Print Resolution window.

Figure 8: Set image print resolution page. 

Here we can see that the X and Y resolution is 300 pixels/in which means that that for every inch of paper we have, there will be 300 pixels printed. So if we have 6,000 pixels along the top and 4,000 along the side that means we must have 6,000/300 = 20 inches along the top and 4,000/300 = 13.333 inches along the side… and if we look at the print size in the window above we can see that has already been calculated for us.

20 by 13+ inches is quite a large size. How can we print it out smaller to fit on our page? We need to fit more pixels into each inch, and since the size of an inch can’t change then the size of the pixels must change. That is done automatically for us by GIMP or Photoshop, or whatever image processing software package you are using. Let’s say we set our image resolution to be 600 pixels per inch. In that case we can see that the print size has adjusted to a much more manageable 10 x 6.67 inches. The resolution changes as the physical image size changes because the number of pixels that make up the image are being spread over a greater or lesser area.

Figure 9:  By increasing the number of pixels per inch we can fit our image into a smaller area of the page.

PC monitors are generally considered to be low resolution devices meaning that images look good on screen even if they have a very small total number of pixels. This reduced number of pixels also allows images to load faster leading to an overall better user experience. But if you try to print it out, you may be disappointed at the tiny image that emerges from your printer. Printers are high resolution devices and require an image to have a resolution of about 300 pixels per inch to look sharp and to be of a good quality. 300 ppi is generally accepted as the resolution for professional quality printing, but that number is increasing all of the time. There are many great articles and tutorials about this and other aspects of digital objects found on the Digital Photo Essentials Tutorial for anyone new to the world of digital photography or photo-editing.

Best of luck with your New Year's Resolutions!

Christina Duffy (@DuffyChristina)
Imaging Scientist

Collection Care has excitedly accepted delivery of a new hyperspectral imaging system. The system is designed specifically for archival and cultural heritage imaging for the purpose of revealing hidden and faded information. Digital imaging experts MegaVision, who are based in California, design the system. The EV^TM camera includes MegaVision’s Monochrome E7 50-megapixel back, computer controlled shutter and aperture, and custom hyperspectral parfocal lens, which is responsive over the entire range of silicon sensitivity.

Testing of the MegaVision system, image shows a light brown table with the imaging system ontop, to the left of the imaging system is a laptop and on the right is a book on top of a sheet of plastazote. Either side of the table are LED sidelights with diffusers, the stands of the sidelights are yellow and black.

   Testing of the MegaVision Cultural Heritage EV^TM Imaging System showing LED sidelights with diffusers, and the E7 50 MP digital camera back on vertical mount

The system integrates two previously disparate imaging capabilities: high-resolution photography and multi-spectral imaging. Images are captured over 12 spectral bands from the near ultraviolet (365 nm) to the near infrared (1050 nm). Captured images are used for preservation and scholarly studies of British Library collections on materials such as parchment, paper, papyrus, inks and other constituents of cultural items. A series of palimpsests (parchment from which writing has been erased and overwritten) and Treasures of the British Library have been identified for imaging, which will take place in the New Year.

Cropped black and white image of a section of a Syriac manuscript showing evidence of previous writing under text.

 Evidence of palimpsest detail under UV illumination in this Syriac manuscript (OMS Add 14623)

The MegaVision system replaces the Forth Photonics MuSIS system, which was purchased in 2004 for work on the Codex Sinaiticus project, and has found many applications since. MuSIS creates spectral bands using band pass filters to filter the light after it is reflected from the collection item. The MegaVision system uses narrow-band LED illumination, which subjects the collection items to only the required light energy to expose the sensitive unfiltered monochrome sensor. The LED panels are configured with visible, UV and IR bands. This selective illumination process significantly reduces the light energy falling on collection items, and has the added bonus of looking very cool indeed!

Green illumination showing stand and led infusers saturated in green light.

 Green illumination: Narrow-band LED illumination subjects collection items to different light wavelengths (red, green, blue, cyan, amber, UV, IR)

MegaVision's Photoshoot^TM digital image capture software controls all aspects of capture as well as controlling a colour wheel which allows additional light modifications such as filtration to isolate fluorescene in concert with UV illumination.

The technology has been internationally heralded for its use on the Archimedes Palimpsest Project, the Gettysburg Address and the Waldseemüller map, while data is still being captured from St Catherine’s Monastery in the Sinai Desert. The datasets will become digital assets of historical and scientific value in their own right, and can be further processed to enhance regions of interest.

This is a landmark purchase for Collection Care showing the committment we have to furthering the understanding of our collections and the importance of science and research in archival institutions. The quest for information recovery and discovery continues! 

Christina Duffy (@DuffyChristina)

Imaging Scientist