Over the centuries, many visitors have found Knole to be a dark house. Back in the 1600s, the diarist John Evelyn was apparently so depressed by greyness of ‘this great old fashioned house’ that he had to hurry out into the sunlight. Today, some of our visitors still comment on the Knole’s often shadowy interior.



A house that ‘smoulders rather than sparkles’.


Many find this atmospheric lighting an integral part of Knole’s unique charm. But for the Conservation team, monitoring and controlling the light levels in the house is a key part of how we look after our fantastic collection. Obviously, we want our visitors to be able to see the beautiful objects. However, displaying our collection while minimising the damaging effects of light, is a constant challenge.



This suite in the Brown Gallery was once a vibrant purple colour but has heavily faded in the light. 


When light falls on the surface of an object it provides energy. This induces a chemical reaction in the molecules of the material, which causes physical changes including the structural weakening of the fibres and a change in colour. The damage caused by this reaction is cumulative and irreversible. How vulnerable different materials are to light varies, but textiles particularly are highly light sensitive. We have the largest collection of English Stuart furniture in the world to have survived. It is internationally significant and we want to ensure that these magnificent pieces can be enjoyed for generations to come.

A key part of our work involves monitoring the light levels in the show rooms. If you look carefully at some of our furniture, you may notice small rectangular cards with a square of blue wool in the centre. These are called dosimeters and we use them to monitor the effects of light. They are placed on or near light sensitive objects and left in position for a year. Part of the blue wool is exposed while the other part is protected. When the dosimeter is removed and sent off for analysis, a measurement is made of the degree of fading. How much the blue wool has faded depends on the amount of light it has been exposed to. The conservation team also conduct regular checks to measures both the UV and the intensity of the light (lux) and we have two Hanwell LUX/UV monitors on the east and south sides of the building, which send back information to a computer in the office.



Knowing the fade rate of the blue wool allows us to accurately measure how much light objects and rooms are exposed to.



The most effective way to protect our collection is by preventing it from being exposed to too much natural light. We now have case covers on the furniture in the Spangled Dressing Room, to protect the incredibly fragile and deteriorating fabric. Historically, case covers have been used to protect special pieces of furniture in grand houses from the ill effects of light and dust. Should an important person come to visit the covers could be removed to reveal the textile underneath. Our red custom cotton case covers have been carefully made by upholstery conservator Heather Porter to ensure that each piece of furniture gets the individual protection that it requires.



One of our brand new case covers in the Spangled Dressing Room


The most damaging part of the light spectrum is ultraviolet (UV) and sunlight contains a high proportion of UV. Where possible we try to filter UV out by using a film on the windows of the show rooms. The light levels in the rooms are kept low and we only expose the rooms to light when it is necessary. However, the current electric lighting in the show rooms is inefficient and ineffective, meaning our collection is often poorly lit. This is something being addressed by the project. A scheme for new lighting has been designed by Sutton Vane Associates. Historic light fittings will be fitted with LED bulbs, which will not only significantly improve the presentation of the show rooms but will also help protect our collection.


This is from a trial conducted at Knole in the Brown Gallery. You can see how the proposed LED lighting will not only protect the vulnerable materials but really highlight our fabulous collection.

Constructing Case Covers

The Spangled Dressing Room at Knole is home to a wonderful set of c.1670 walnut furniture that includes six stools and two chairs. These pieces were originally housed at Whitehall Palace until they were brought to Knole by Charles Sackville, 6th Earl of Dorset (1638 – 1706).

Having sat in the poor environmental conditions at Knole for over 300 years the delicate silk damask material is in a pretty bad state. It was decided that in order to protect the incredibly fragile and deteriorating fabric that protective case covers needed to be made.

If you look closely you can just about see conservation netting. A fine colour matched net that has been added to attempt to stabilize the fraying silk.

Historically case covers have been used to protect special pieces of furniture in grand houses from the ill effects of light and dust. Should an important person come to visit the covers could be removed to reveal the textile underneath.

Our 17th century furniture in the Spangled Dressing Room is in such a fragile state that many of the red threads have faded completely to beige. With dust from generations of visitors and light streaming through the windows the stools and chairs the silk has powdered on the surface in places.

You can see here the fading and shredding of the delicate silk.

New case covers have been made over the past several months to protect the fabric of the seats. Red custom cotton case covers have been carefully made around the furniture by upholstery conservator Heather Porter. Each case cover has been custom fitted in situ at Knole so that each piece of furniture gets the individual protection that it requires.


The newly fitted cotton case cover contrasting with the uncovered pillow.


The case cover project was to design and make covers for display that resulted in an improved visitor experience. It did not involve treatment to any part of the extant upholstery.  After the project the fragile condition of the upholstery below remains the same, but with increased protection from dust and light.


Heather has primarily used a burgundy custom woven cotton fabric to make the covers.

As you can see, the finished results are fantastic. The new case covers not only protect the vulnerable upholstery but really add to the effect of the furniture. The material sets off the rest of the furniture allowing you to appreciate the fine carving of the walnut frame in a new way.


Now that we have new covers on this suite it’s always possible more work can be done in the future. Heather has already returned to examine the possibility of doing some work on the upholstery of our Reynolds Room chairs as well!

Keep checking the blog for more.

Monitoring the Great Stairs environment

The Great Jacobean Staircase at Knole, Sevenoaks, Kent

The Great Staircase was entirely remodeled by Thomas, 1st Earl of Dorset, between 1605 and 1608. It formed a key stage in the formal procession of the family and their guests from the Great Hall to the state rooms on the first floor.
The Great Staircase at Knole was remodelled by Thomas, 1st Earl of Dorset between 1605-1608 at Knole, Sevenoaks, Kent

The wall paintings decorating the main staircase at Knole are rare and very important survivals of Renaissance decoration. Dating from about 1603, they are one of only two complete schemes which survive from this period (the other is at Harrington Hall in Worcestershire) and presage the development of sumptuous painted staircase schemes in the late 17th or early eighteenth century, as seen in the King’s Apartment at Hampton Court Palace.
The Great Staircase from the landing at Knole, Sevenoaks, Kent

The paintings were executed in oil on plaster and have been unstable from an early period. Oil paint tends to lift and flake in the English climate, and their location also makes them particularly vulnerable to damage by touching. Flaking eventually leads to loss of the paint, seen in the white spots over the painted balustrade. The following images illustrate some of the damage and earlier remedial conservation repairs that have taken place over the years:

Areas of paint flaking revealing the plaster underneath

Areas of paint flaking revealing the plaster underneath

Cracking in the paint surface

Patches of previous repair, some of which are now failing and the paint is flaking off again

Patches of earlier repair, some of which are now failing and the paint is flaking off again.

As a part of our Inspired by Knole conservation project we are currently undertaking some extensive environmental monitoring of the staircase, internally and externally. We have placed temperature and relative humidity sensors on the external wall of the staircase and on the inside wall.

The external sensor, on the east facing wall

One of the internal sensors, on the north wall. The second is positioned on the east wall

One of the internal sensors, on the north wall. The second is positioned on the east wall

This will allow us to monitor what the temperature and relative humidity levels of the external wall surface and the internal wall paintings. Using time lapse photography we are also recording where direct sunlight falls on the external and internal walls.

The time lapse camera recording direct sunlight on the external wall of the Great Stairs.

The time lapse camera recording direct sunlight on the external wall of the Great Stairs.

 Our conservators who came to install the monitoring equipment also took some thermal images of the walls, another method to record the temperature of the wall surfaces.

Inside thermal imaging shot

Inside thermal imaging shot.


We are also monitoring another two wall surfaces to draw comparisons with the Great Stairs. The Spangled Bedroom, with new render and insulation; and the Brown Gallery which has relatively new render but no wall insulation. In these locations we have a temperature and relative humidity on the external surface and in-between the render and internal plaster. By monitoring the effects of new render and a wall with and without insulation, this will help us decide what the best method of protection will be for the Great Stairs wall paintings.

Alex, Emily, Lucy, Melinda, Sarah and Zena

Conservation Wars…

…is the title of our new conservation module that we are in the process of developing for our school visits. Together with Knole’s Learning Officer, Barbara, her team of volunteers, myself and Zena and Alex our Conservation and Engagement Assistants, we have designed a module that can fit in to the school visit day alongside the other activities available for schools to choose from.

The first slide in our presentation for the school module.

The first slide in our presentation for the school module.

At this stage we have devised the module for key stage 2 (ages 7 – 11).  Our aim is to have a module suitable for all key stage groups.  We began with deciding how much information about preventive conservation we wanted to try to teach.  Looking at the agents of deterioration we decided to introduce this as the theme of the module but only focus on three of the agents that are very relative to Knole; light, dust and touching, and pest insects. Barbara came up with the brilliant idea of the Conservation Team battling against the enemies that are the agents of deterioration. We thought this might be a good concept that would capture the children’s imaginations.

 We’ve put together a short presentation (mostly images) to introduce the subject of conservation and the agents of deterioration to the school group.  It is aimed that this will last no more than 15 minutes (we’re still testing it). The rest of the session is all hands on and interactive with three activities based on light, pest insects and touch and cleaning. The group would be split in to three smaller groups. Each activity lasts 10-15 minutes, and the activities are swapped round each group.

The pest insect activity involves the children making their own pest insect traps, looking at insects we’ve collected from around the house and matching up the insect and mammal life cycles.

Making pest traps

Making pest traps

The light activities include taking light readings in the room, making a blue wool dosimeter (light monitor), and seeing how much ultraviolet light there is in sunlight coming through the window.

Two examples of dosimeters we use and a 'home made' dosimeter.  We use a special light sensitive photogtraphc paper that changes colour / fades in the light within minutes, so the children can see the reaction happen instantly.

Two examples of dosimeters we use and a ‘home made’ dosimeter. We use a special light sensitive photographic paper that changes colour / fades in the light within minutes, so the children can see the reaction happen instantly.

The beads are covered in a chemical that react to UV. One half of the clear perspex have a UV filter on it (the side where the beads are cream) and one half with no filter (the side where the beads are pink).

The third activity, focuses on physical damage from human touch and cleaning the group will use handling frames to see how different materials can deteriorate from touch, investigate dust samples and have a go at cleaning different objects including some dusty textiles.


Last week we delivered the session to the learning team volunteers to see what they thought of the module.  They gave us some great feedback and now we’re making a few revisions.  We hope to trial the module with a school group soon.


Knole Unwrapped 2014…

…Book and Archive Conservation in the Gatehouse Tower

The Gatehouse Tower, viewed from within Green Court.

Today the Gatehouse Tower at Knole looks almost exactly as it would have done at the beginning of the seventeenth century. However this lack of significant change to the exterior is not reflected in the interiors which have been altered over the years to serve a number of different purposes ranging from accommodation to storage.

In the 20th century the rooms in the Gatehouse Tower were used by Edward (Eddy) Sackville West, 5th Baron Sackville. During the period from 1926- 1940 Eddy occupied these rooms just as his rooms at Eton or Oxford, they were never used as his permanent home. After Eddy left they were used by Frank Mason, an Estate worker and finally went out of use in the 1960s.

Eddy’s room in the Gatehouse Tower.

The first floor rooms still remain the same painted decoration from Eddy’s time and the bookshelves still house a collection of his books and papers. The room above has not survived as well and at some point the ceiling was removed. In the 1960s a collection of large folios of prints and outsize volumes from the main library were moved here, presumably to make some space in the library.

Second Room of the Gatehouse Tower.

Some of the books currently stored in the tower.

The collections of books, prints and papers had never been closely looked at and only recently came on loan to the National Trust. The collection initially has been catalogued. A professional cataloguer and a team of volunteers from Knole have been steadily working through everything listing, photographing and recording on COPAC and National Trust Collection Management System.

Following on from the success of last year’s Knole Unwrapped Project, this interesting collection of books, prints and papers was felt to be the ideal subject for Knole Unwrapped 2014. The collection urgently required condition recording, conservation cleaning and safe rehousing to enable it to be moved into store prior to building repairs to the Tower.

Learning from last year’s programme it was felt, with this projects focus being purely on books and paper, volunteer supervisors could be trained to run the programme.

Caroline Bendix, National Trust Library Conservation Advisor, gave a one day training course on basic conservation and stabilisation techniques for books to the supervisor group. This was then rolled out to the participants.



Book conservator, Caroline Bendix, demonstrates how to hold book open, this is incorrect.

The correct position to hold open a book, no more than a 90 degree angle.

The correct position to hold open a book, no more than a 90 degree angle.


Knole Unwrapped 2014 will have three sessions each lasting ten weeks with a new group for each intake. The group signs up for one day per week for ten weeks, and as well as carrying out essential documentation and conservation work, will receive training and opportunities to learn more about Knole and its collections.

Brushes used for book cleaning. Pony hair brush on the right for the book exterior; hogs hair brush on the left for book interior / pages.

Book cleaning practice.

Book cleaning practice.

The first session is now half way through and so far has been a success with the participants thoroughly enjoying their work and making great progress. The group is a wonderful mix of people from different backgrounds with a wide range of skills and knowledge: from a retired librarian to a student studying Musical History; existing Knole volunteers and a student applying to Conservation courses. No prior knowledge or skills are asked for when applying to participate, just an interest in books and conservation and a desire to learn.


Wheat starch is used for basic remedial repairs to torn and damaged boards and the corners of book boards.

Practicing repairing a book cover with wheat starch.

Practicing repairing a book cover with wheat starch.

Once building repairs to the Tower have been completed the collections will be reinstated and the Tower will open to visitors.



Caring for photographic materials – part 3!

All types of objects are affected by one or all of the agents of deterioration, and photgraphic materials are no different.  Photogrpahic matrerials are most sensitive to the incorrect tempertautre and relative humidity, light and air pollution.

Light causes the images to fade leading to eventual loss of the image.  Some photographic process will result in fading occurring more quickly as they are more light sensitive than others.  Ultraviolet light is the most dmagaing part of the light spectrum and so must be ellimated from the location a phptpgraph is to be displayed.  This can be done by applying a special film on to the window glass that anbsorbs the UV out of the natiral light coming in. While on display photographic materials should not illuminated above 50 lux and they should not be left on permanant display. 

Light damaged photo.  Image copyright of Sarah Allen.

Light damaged photo. Image copyright of Sarah Allen.

High and fluctuating temperatures exacerbates image fading and accelerates the rate of deterioration.  Similarly with relative humidity high and fluctuating levels cause the most damage.  Physical and chemical damage will occur if the environment is too humid, and if too dry physical damage such as cracking, fissuring, peeling will occur. Different types of photographic materials should be stored at different temperatures:

– Subzero (-20º – 0 ºC): Cellulose nitrate, cellulose acetate, early colour film & prints
– Cold (0º – 8º C): otherfilm based negatives
– Cool (8º – 16º C): glass/metal based photos
– Room (16º – 23º C): well processed black and white prints.

Pollutanats from both the environment, storage materials and the photographs themselves can cause deterioration. Pollutants can cause yellowing of prints and oxidisation of silver. Photographic processes that use cellulose acetate can give off acetic acid when they are degrading. The following methods can be employed to prevent damage by from pollutants:

– Reduce pollutants by using filters if possible
– Increase air movement to avoid microclimates
–  Use good quality housing to mitigate effect of poor air quality

As if all of the above wasn’t enough to cause deterioration there are biological and physical factors to add in to the mix too!  Mould and pest insects can cause damage:

Mould stained photograph.

Mould stained photograph.

Silverfish damage to a photograph.

Silverfish damage to a photograph.

Common furniture beetle (woodworm)  damage.

Common furniture beetle (woodworm) damage.

And then there’s us of course!  Poor handling, storage and display can all lead to physical damage, inlcuding breakages and tears.  


Preventive conservation housekeeping plays a key part in looking after photographic materials, as it does with any collection.  Here are some of the basic steps that should be taken:
 – Keep research and storage areas clean. Use a vacuum fitted with a HEPA filter
 – Regularly check for mould, insect or rodent activity
 – Avoid using household cleaners
 – Place away from heat/water sources (e.g. radiators)
 – Do not store photographs near photocopiers
 – Avoid using carpets in storage areas if possible
 – Do not store photographs in freshly painted rooms

So in summary, some key points to remember for the care of photographic materials:
  – Get to know your collection;
  Identify the different photographic processes in your collection, particularly those susceptible to degradation.
  – Handle items correctly;
  This is one of the main causes of damage to photographs but one of the easiest to mitigate.
 – Monitor the environment – and improve where needed; 
  Be aware of poor quality primary enclosures and containers, other possible contaminants and biological activity. Monitor environmental conditions to ensure they’re suitable.
– Carry out regular condition checks;
  Monitor the condition of the collection regularly, consulting a specialist conservator if there is cause for concern.

Alex, Emily, Lucy, Melinda, Sarah and Zena

Caring for photographic materials – part 2

Once you know how to handle photographs the next key step is being able to identify them.  To preserve an object you need to know what it is!  Although this isn’t necessarily easy when there are over 1500 types of photographic processes.  It sounds obvious but you must look a the object, not the image. Sarah advised us to go through a process of elimination to help us identify the process that happened to produce the photograph or negative:

• Is it a true photograph or photomechanical?
• Is it a positive or negative?
• Is it paper-based or otherwise?

Slide copyright of Sarah Allen

Are you now wondering what photomechanical means?  It isn’t a photograph but can look like one.  The best way to identify that isn’t is using a magnifying glass.

It is ink on paper, made up of either a series of dots (letterpress halftone), gridlines (collotype) or squiggles (photo gravure).

So what are some of the photographic processes…?

> Negatives:

– Paper negatives: were in use from 1840 to 1865, though can be dated to later.  The glue is in the title, they will unmistakably be on paper.  Sometimes they are waxed for to make the details of the image clearer, this can make the negative more translucent.  They were often used by armature photographs and pioneers of photography like William Fox-Talbot.

– Glass plate negatives:
Wet collodion glass plate negatives: used between 1850 and 1900. There appearance would be a creamy brown colour and not uniformly coated with emulsion. They provided high quality prints as collodion emulsion has very small silver salts in it allowing prints to be blown up without losing definition. They could only be processed by professionals with a dark room on site. You can very often see a corner thumb mark showing previous handling.

Wet Collodian Negative

Wet Collodian Negative

Wet Collodian negative and print. Images copyright of Sarah Allen

– Gelatine dry plate negatives (1870-1920) look very black and white and the emulsion is applied by machine.  This had been developed by George Eastman of Kodak.  His work led to a rise in amateur  photography as ready made negatives could be bought in advance. Gelatine dry plate negatives are still sometimes used in astronomical photography today.

– Film negatives:
Cellulose nitrate negatives (1885 -1950s). Cine film was also made using the same process.  These negatives / or cine film can be highly unstable if allowed to deteriorate or are in poor storage.  Signs of deterioration include an acrid smell, a sticky orange/brown substrate and powder being formed. Deteriorated cellulose negatives can self ignite or explode. Eventually because of the risks that nitrate posed cellulose negatives were banned.

Deteriorated cellulose nitrate negative.

Deteriorated cellulose nitrate negative.   Image copyright of Sarah Allen.

– Cellulose acetates in use from 1920 to the present day. A more stable negative in that it is not a fire risk.  Signs of deterioration include a strong vinegar smell, wrinkling and channelling of the different layers. It is considered a health and safety risk however if in poor condition as they can give off acetic acid.

– Polyester negative films are the most recent negatives to have been developed.  PET from 1955 and from 1996 PEN.  Both still in use today and extremely stable meaning that it does not deteriorate, as far as we know!

> Positives

– Non- paper based positives are unique and no copies could be made.

– .Daguerreotypes 1840-1860.  Named after its inventor Louis Daguerre.  They are made from silver plated copper sheet, which is highly polished. They look distinctively mirror like. They can be both positive and negative depending on the angle it is viewed from. It was a high end product most popular in USA but not England or elsewhere. The patent for the use of the Dauerrotype was free for the entire world except England, making them costly to use for British photographers and a rare object today.

– Wet collodion positive (UK) or ambrotype (USA, named after American inventor and photographer, James Ambrose) 1852-1865.   One side of a very clean glass plate is covered with a thin layer of collodion, then dipped in a silver nitrate solution. The plate is exposed to the subject while still wet. (Exposure times vary from five to sixty seconds or more depending on the amount of available light.) The plate is then developed and fixed. The resulting negative, when viewed by reflected light against a black background, appears to be a positive image: the clear areas look black, and the exposed, opaque areas appear light.  There is often 3D effect from different layers.

Image side of wet collodion positive.

Reverse, blacked out.

– Tintype (or ferrotype).   Made on sheet of blackened iron which is then varnished, but often has an uneven coating.  They were cheap and cheerful.  Using a magnet is the easy way to identify if it is a tintype.  An obvous clue to look out for signs of decay is iron oxide (rust).  The dates at which tintypes were used can be a bit ambiguous. They were used initially during the 1860s and 1870s, but lesser use of the medium persisted into the early 20th century.

A magnifying glass with a light is a very useful tool when trying to identify photographic processes.

> Paper based positives:

> One layer positives = one layer of paper with photographic emulsion sat in paper fibres. The fibres can be clearly seen and it will have a very matt surface.

– Salted paper prints: 1840-1865. Warm brown colour in appearance, with a matt surface.  They did not produce crisp images.

– Platinum prints: 1880-1930
Platinum salts was used instead of silver salts as they were more stable. The image would have a cool slate grey colour with a matt surface.  This processed produced very stable prints with little or no image degradation.

Platinum print. Image copyright of Sarah Allen.

– Cyanotype prints: 1880-1920.  As the name suggests these prints have a distinctive blue colour, again with a matt surface.  They were easy to produce and therefore used by amateurs quite often.  They are sensitive to alkaline environments.

> Two layer positives = the paper fibres are only partially visible. The surface has some gloss and a surface coating is discernible.

– Albumen prints: 1855 -1920s The binder used is egg white from hens eggs instead gelatine. The prints will  have a semi-gloss surface and tend to fade to a warm colour. Very often there will be cracking across the surface.

Albumen print. Image copyright of Sarah Allen.

– Carbon prints: 1860 -1940s. A pigmented process with gelatine instead of silver salts. The print will have a semi gloss surface with a relief visible.  This is caused where the darker colours in the print have more pigment than in the lighter areas.  The use of raking light will show this. No image degradation occurs.

> Three layer positives = the paper fibres are completely obscured. Print surface can be anywhere from very matte to very glossy and more than one layer is discernible.

– Gelatine P.O.P (printing out paper):  1880s-1920s.  Prints would have warm tones, monochrome not cool black and white. Usually a glossy finish and they come in many different formats.  They are very sensitive and cannot be put on permanent display, best stored at cold temperatures.

Gelatine P.O.P. Image copyright of Sarah Allen.

– Collodion P.O.P: 1880s -1920s. The prints produced had warm tones, possibly with a purple tinge, and a glossy surface.  They can look like the gelatine P.O.P prints, the use of raking light to show ‘Rainbow’ interference colours helps to distinguish them from Gelatine P.O.Ps.  The prints can become brittle and scratched.

– Gelatine D.O.P (developed out prints): 1880s – present.  They come in many different surface finishes and are very stable. It is the most common black and white processed used in the 20thC. Produced in a developing bath and resulting in very crisp images.

In part 3 we’ll explore remedial and preventive conservation practices for caring for photographic materials.