Mould can grow on any surface, especially in our wet, damp climate! It’s one of the most common and serious causes of damage to our heritage but is largely preventable. NLI conservators often deal with mould on paper and the Patrick Pearse Papers are currently getting some first-aid treatment … Here are some ‘fun facts’ you might not want to know!

Under ultraviolet light mould and inks look different Under ultraviolet light mould and inks look different



Mould is a type of fungus; the main body is made up of fine colourless threads called hyphae, which intertwine to make up a tangled web called the mycelium. Fruiting bodies, in which spores are formed, develop on the hyphae ends. The fluff that we can see growing in established colonies is often the tip of the iceberg. In ultraviolet light, mould fluoresces strange and wonderful colours, revealing the full extent of damage to the paper.

Fluffy brown mould on the surface of a document (MS 21093) Fluffy brown mould on the surface of a document



The air around us has billions of dormant mould spores (nice thought eh!). These tiny particles (1-10 micrometres) land on a surface such as organic materials leather, paper, glue, wood and textiles. The spores will germinate at high relative humidity (70-100%) and an optimum temperature of 24-30º Celsius. In order to grow, mould needs oxygen and food sources. Mould can also digest some synthetic materials such as adhesives, pastes and paints.

Mould has stained this document pink, black and orange Mould has stained this document pink, black and orange



The Pearse Papers showed the direct damage caused by mould growth. Using enzymes, mould decomposed the cellulose and paper size to extract nutrients. As moulds’ hyphae ruptured the paper structure, the items cannot be handled or read without risk of disintegration. Acidic waste products have made the paper brittle and colouring substances excreted by the mould reduces our ability to read these historic documents. This colour depends on the surface substrate and the age of the colony. It can be any colour of the rainbow!


Mould can spread easily and it’s best not to breathe-in mould spores. Visible mould growth was removed with a fine brush into a HEPA vacuum cleaner nozzle under a suction hood. The presence of modern fibres and fragile inks meant treatment of the Pearse Papers was problematic. To denature the spores, an alcohol solution was carefully applied to selected items but this can damage inks so its best for such treatment to be undertake by a trained conservator. The most fragile items were washed to remove acids. Then a very thin tissue lining was applied to support the degraded paper and/or methyl-cellulose size is applied to consolidate the papers fibers. Papers unsuitable for washing were repaired using remoistenable tissue techniques.

Methycellulose size applied to strengthen mould damaged papers Methycellulose size applied to strengthen mould damaged papers


Any risk of new growth will be limited by correct storage conditions of low temperature and humidity. These manuscripts document an eventful period in Irish history at the turn of the twentieth century. The conserved material will be scheduled for digitisation next year and will be accessible for national and international audiences via the NLI online Catalogue

The Pearse Papers Project is funded by the Heritage Council HERITAGECOUNCILMASTER

Mould in your collection?

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Blog written by Gabrielle Vergnoux and Louise O’Connor, NLI Conservators.


By Gabrielle Vergnoux, Conservation Intern, National Library of Ireland

At first sight, an image of “Cork Harbour by Robert Lowe Stopford in 1862”, as is written on the verso, seems to do exactly what it says on the tin. The large marine landscape (29 x 71 cm), from the library’s Prints & Drawings Collection, depicts figures bustling in the foreground, with an expansive vista of ships fading into the distance. Robert Lowe Stopford (1813-1898) was a popular Irish watercolour artist who represented landscapes and marine subjects, so we assumed the image was a watercolour.

Picture under scrutiny: 'Cobh Harbour' after Robert Lowe Stopford Picture under scrutiny: ‘Cobh Harbour’ after Robert Lowe Stopford


The picture, in rich sepia and bistre brown tones below a vibrant blue sky on a thick coated paper, was in fair condition. There was water-damage and dirt across the image on a thick delaminating board. The blue sky colour, which extends onto the board, had also faded from exposure to light.

Thick delaminating board supporting the image (left) A shiny substance in the foreground (right) Thick delaminating board supporting the image (left) A shiny substance in the foreground (right)


After observation, we noticed some odd details. The painterly figures in the foreground were almost ghostly apparitions with fuzzy edges. There were uneven traces of a shiny substance, possible a gum or resin varnish, applied with a brush. The atypical colour balance of very bright blue and the musty browns were even more confusing. We could not see the back of the image, which can often tell more than the front, so before any treatment, we decided that a more in-depth examination linked with research was necessary.

3--Figures-in-foreground-seem-ghostly-apparitions-under-magnification-small Figures in foreground seem ghostly apparitions under magnification


So was it a watercolour painting? Was the date written on the verso correct? Did Stopford, the watercolour artist, create it? Could it even be some sort of reproduction under watercolour over-paint? If so, which printing process could it be? This question is at the heart of our investigation. Let us try to better understand what secrets this curious image might reveal … A lithographic impression is made from a drawing made with thick wax on a stone, based on the principle that the water and the oil do not mix. As one of many economical methods of reproducing artworks from the 19th century, Stopford’s images were reproduced by lithography. So, could our image be a lithograph reproduction? We looked in the NLI Topographical print collection and found similar maritime lithographs after Stopford. We could quickly see that our object lacked the tell-tale grain pattern of the lithographic stone. Besides, lithographs are generally done in black and our object had distinct sepia and bistre tones.

Lithograph reproduction of a watercolour by Robert Lowe Stopford Lithograph reproduction of a watercolour by Robert Lowe Stopford


Having ruled out lithography, we found an exhibition catalogue featuring the original watercolour by Stopford, now part of the Cork Port Authority’s collection. The similarity to our object was striking; the smallest details and imperfections seen on the original were also visible on our object. Even the signature was reproduced identically in the bottom right-hand corner. This fantastic detail meant that our image was not flipped, as happens in printing. The discovery compelled us to think that the image was reproduced by a photographic process. We also learnt that the original was in fact of Cobh harbour and was painted in 1852; so the information written on the verso of our object was somewhat doubtful.

The 1850s were a fundamental decade in the history of image trafficking. For the first time, art publishers had at their disposal numerous ways of reproducing an artwork. But which photographic process had been used to create this image? It was back to the microscope to understand what process was used to reproduce this image. The fuzzy aspect of the edges of the figures continued to confound us. Under magnification, the contours seemed to have been “burned” onto the paper, as if they had been subjected to light exposure. We also noticed a demarcation at the corners of the image, a distinctive element of photographic images. In addition, the sepia and bistre tones are typical colours of early photographic processes and depending on the process used, it was easy to find traces of gelatine or gum on the image surface.

Microscopic investigations! Microscopic investigations!


With the help of the Graphics Atlas database –  – and Care and Identification of 19th century Photographic Prints, we compared the date and the documented magnified images of the different processes. We found several possible matches; gelatine POPs was soon ruled out as it was extensively used for commercial portraiture, fine aquatint grain was considered, but our image lacked the smooth gradation of tone this process normally gives. The salt paper process (with gum arabic highlights) gives a similar effect to our ghostly figures but the paper used in that case is generally matte and our paper is glossy.

5-small Our object (left) and the original (right) in Cork Port Authority


Lastly, the gum bichromate process, a contact print process based on the light sensitivity of dichromate salts, was considered. Known as the pictorialists’ favourite process from 1885 to 1915, it’s capable of rendering painterly images from photographic negatives – which explains why we have the image in the “positive” sense, with the signature on the right.  This gum bichromate process permitted the creator to use painters and photograph’s tools: brushes, pigments and negatives, to directly intervene and give a personal interpretation of the reproduced image. Furthermore, a coated paper that can withstand repeated soakings was used, and this is the type of paper that we have on our object.

Until the 1960’s, most photographs were the result of an impression by contact, which means the negative was the exact dimensions of the original. The gum bichromate process generally has at least two steps. Firstly, glass or paper with a light sensitive emulsion, the same dimensions to the original, and the original are “sandwiched” together. The sandwich is exposed to ultraviolet light such as mercury vapour lamp, a common fluorescent blacklight or quite simply, under the sun. By exposure, the emulsion hardens and becomes insoluble creating a reversed or negative copy of the original on the paper or glass. Then a new blank sheet of paper is prepared with gum arabic mixed with pigment of choice and bichromate. The negative is then sandwiched between a sheet of glass and the prepared paper, and everything is exposed to light again. This creates a positive image on the coated paper. Therefore the paper used for the printing, the ghostly image, clearly seen under magnification, and the surprising dimensions match the gum bichromate process.

In our object, the foreground is produced in this way, but the background is clearly painted in watercolour. Why then did our artist decided to add watercolour to the photographic print? There are two possibilities. Maybe our artist hid the parts he did not want to print on the negative, in order to give free rein to his creative talents. Or, maybe the rendering of the printing of the foreground was not satisfactory and he decided to complete the image with watercolour. The final artist step seems to be the addition of a highlighter, such as glycerine, gelatine or more gum arabic, onto the figures in the foreground, to darken tones and create more contrast.

It remains to be understood by whom, when and why this image was created.  We cannot know if the image is contemporary to the drawing or if it was created after. We can wonder if Robert Lowe Stopford or a family member was responsible, seeing as access to the original watercolour or at least its negative was essential to the creation of our object. It’s also plausible that an anonymous artist created this object as a “kitchen-sink” experiment in the early 20th century as he liked the subject!


With thanks: Clodagh Neligan ACR, Senior Paper Conservator, Glucksman Conservation Department, Trinity College Library and Gillian O’Leary, Port of Cork Company –

The post of Conservation Intern is jointly funded by the National Library and the Heritage Council.



Only very cool conservators get to work on the conservation equivalent of CSI. Yes, it’s fun to wear white coats, flash the ultraviolet light around and talk abut acidity (for us, anyhow!), but the reality of preserving our paper heritage collections is somewhat more mundane. That is until we must deal with LOTS of mould. Then things become somewhat more exciting!


Preservation of the Pearse Papers, funded by the Heritage Council, was recently completed. Conservation student volunteer Valentina Giunta, from Tor Vergata University in Rome, worked on re-housing and surface-cleaning the collection.

 Conservation student volunteer, Valentina Giunta, re-housing the Pearse Papers collection


Re-housing the papers was essential to their preservation. Normal stationery supplies are not suitable for long-term storage. They are made from wood-pulp paper that will very quickly turn acidic, creating an acidic ‘micro-climate’. The manuscripts in these folders can absorb the acids, speeding up their degradation. The new grey folders are acid-free, lignin-free and with an alkaline buffer for ‘permanent’ storage. While the new folders may not seem very exciting, they will actively protect the items from degrading.

Spot the difference-new and old folders


A condition assessment found that many papers are mould-damaged. This has resulted in extreme discolouration, ink damage and embrittlement. Some of these sheets are very fragile and cannot be handled safely. The mould and water damage has even resulted in the cementing together of each sheet in one booklet from Cumann na Poblachta (a precursor to Fianna Fáil political party) signed by Margaret Pearse in 1922.

Mould & water damage has resulted in cementing together of each sheet in this booklet from Cumman na Poblachta Mould & water damage has resulted in the cementing together of each sheet in this booklet from Cumann na Poblachta


Prior to re-housing, these mould damaged items have been isolated for treatment. The Next step is to plan the conservation treatment of over 450 sheets, which will be undertaken this summer. This will involve solubility testing of all inks, photographic documentation and lots of scratching of heads while we decide how to deactivate mould spores and strengthen and repair all the papers. Stay tuned for more updates on the project this summer.  Now to where did I leave my ultraviolet light…

This letter is severly damaged by mould causing extreme discolouration ink damage and embrittlement Letter severely damaged by mould causing extreme discolouration, ink damage, and embrittlement


Blog written by Louise O’Connor, a Conservator at the National Library of Ireland.