Spot checks!

One of the most important things we do at Knole is keeping an eye on the environmental conditions in the Showrooms. We do this through a combination of ways. Our primary method is using individual monitoring sensors in each room that send a regular signal back to the office detailing the Relative Humidity (RH) and temperature in each space. By this method we can keep an up to the minute record of what’s going on.


Our regular ‘Hanwell’ environmental monitors. This one is in a storage space and is showing an RH reading of 58%, right where we want it.

However, because of our current project and the work going on to improve the lighting, conservation heating and all sorts of other things it means that we don’t have proper radio monitors in some rooms right now.



RH in some rooms sometimes reaches worryingly high levels. It’s essential to keep a good watch on what’s happening.


This means that our secondary method become more important and we have to do it more regularly. This method is using spot checks. Usually we go into each space in the showrooms and store rooms every two weeks to take temp, RH, lux and UV readings to make sure that our automatic monitoring is consistent with our handheld sensor.

While the sensors are gone in the second half of the house we send the intrepid Zena in with a hard hat and a monitor to take readings every week. This way we know what kind of conditions the historic showrooms are facing on a day to day basis in all weathers.


Zena taking readings in the Ballroom

Oh the humidity!

One of the most important elements of conservation is making sure that our collection has the best possible environment to live in. In a house like Knole this is very difficult. It’s a large building with no heating or other environmental control. This means that the house can be at the mercy of the elements. Humidity and temperature rise and fall with the weather with no way for us to control it.

photoCondensation in the Second Painted Stair caused by high humidity (RH)

As part of the conservation project at Knole we will be having special conservation heating installed in the showrooms here. Sadly for our visitors and volunteers this does not necessarily mean that the house will be toasty and warm in winter! The heating will purely be there to control the RH (Relative Humidity) of the rooms. Relative humidity is one of the biggest problems we face here at Knole. When it is too high it causes condensation to build up on vulnerable surfaces, attracts dust and makes a perfect home for mould. It can also create perfect conditions for all sorts of pests such as woodworm and deathwatch beetle. When it is too low it can cause some materials to contract and crack, veneers to lift and glues to fail.

Because of the importance of RH and temperature we have to keep a very careful eye on conditions in the showrooms. If there are particular anomalies such as high RH where it is usually lower we can investigate what has happened. Perhaps there is a leak or a heater has failed. Although we don’t yet have control over the showroom temp/RH we have been able to have some control in some behind the scenes areas at Knole. We have special humidistats in special stores that will react to the Rh in a room and turn on heaters when necessary.


 Humidistat in the storerooms.

The primary method we use to monitor RH is our Hanwell environmental monitoring system. If you visit Knole you may see the sensors dotted around the galleries.


Here you can see the Painting Store monitor. It has an LCD display showing you the RH and temperature at the time.


Each room has a box and each box is equipped with a transmitter that relays the information it’s gathering to a computer in the office. This then plots a graph that allows us to see trends and patterns in individual spaces.

Within the National Trust we try to aim for an RH level of 40-60%. This represents the amount of water vapour present in air as a percentage of the amount needed for saturation at the same temperature. Because National Trust collections are often so varied and in historic settings there is no perfect RH that is ideal for all materials but this range gives us the best chance.

To make sure we have the most accurate readings possible we also take spot readings on a regular basis. This involves taking a handheld RH/temp monitor into each space and taking an extra reading. This is a good way to make sure we are obtaining accurate information. This is also our primary method of keeping an eye on RH/temp in the part of the house currently undergoing conservation work ready to be opened again next year.


Here is Zena taking environmental readings in the Ballroom during the conservation work.

Knole suffers with frequent high RH which will be addressed when we have our new conservation heating. Until then we do what we can!


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.

A Day in the Life of the Conservation Team


In a sense the title of this blog is a bit of a misnomer, because no two days at Knole are ever the same. Every day is different and it’s partly the variety that makes Knole such an exciting place to work. However, it’ll hopefully give you a flavour of what we get up to, day to day, in order to look after this magnificent house and its collection.

The work of the conservation team changes with the seasons. Over winter, when the house is closed, we are busy working in the show rooms, condition checking and deep cleaning the rooms and the all the objects in readiness for re-opening.


Zena cleaning the textile of a chair during winter before carefully condition.


This winter has been a bit different because of the project. Although the first half of the house (from the Brown Gallery to the Leicester Gallery) had its normal winter clean, the second half of the house (from the Ballroom to the Cartoon Gallery) was emptied in preparation for the project work that will be going on in there this year. You can see some of the collection from the second half on display in our Great Store.

Now the house is open, our routine changes. In the morning, we spend the first few hours when the house is closed getting the show rooms ready to open. Every room is vacuumed to pick up anything left behind by our visitor’s footwear the day before. We also dust any flat surfaces in front of the rope barriers and check to make sure that no cobwebs have appeared overnight. Any glass is cleaned to get rid of dust or finger prints. The blinds are set, the curtains are opened and then we’re ready to welcome our visitors for the day.



One of several long galleries at Knole that need careful attention every single day.


There are several reasons why we do this daily clean in the showrooms. Obviously we want the house looking its best, so people can fully appreciate the incredible collection that we have here. But it’s also a vital part of the preventative conservation work carried out by the conservation team. Monitoring the environment and general good housekeeping is the first step in combating the deterioration of our unique historic collection.

The afternoons at Knole vary hugely. Some days we are in the house working on various objects in front of our visitors. These conservation engagements can involve anything from textile cleaning to treating for woodworm and are a great way to show the public how we care for our collection at Knole. Other days we may be monitoring the environmental conditions in the show rooms or polishing door brass. But one thing’s for sure, no two days are ever the same!


Injecting a pesticide to treat for woodworm. Something we do fairly frequently!


Thanks for reading!



Today we’re looking at yet more exciting work in the Spangled Bedroom at Knole. This time it’s all about tapestries! With the bed temporarily living in the Great Hall ready for its own journey away we were able to take down the final two tapestries leaving the walls completely bare. These tapestries went through a careful cleaning and documenting process before being sent off to the De Witt in Belgium. This is a specialist tapestry workshop where the tapestries have been carefully cleaned before being returned to Knole. For a better understanding of how the tapestries were cleaned in Belgium then have a look at our previous blog post ‘How Do You Wash Your Tapestries?’.

The final two tapestries arrived home this morning and have been placed, still rolled and packed, back into the Spangled Bedroom before the next stage of their journey can commence.

Sue and Alice hard at work on one of the tapestries

Sue and Alice hard at work on one of the tapestries

Some of you may remember when we prepared the first tapestries for travel in November 2014. Now that the Spangled Bed has been removed from the room there is plenty of space to work in now. This meant that we were able to set up our tapestry tables right there in the room.

This has a few benefits for us. To start with it means that we don’t have to roll the tapestry, transport it up to the Needlework Room (up some very steep and narrow stairs!) and then unwrap it again. Anyone familiar with the National Trust’s 9 agents of deterioration, to be found in our Manual of Housekeeping will know that the less we move any object the better. Every time an object is handled it increases the risk that it will somehow be damaged.

By taking our tapestries straight down onto the tables to be worked on we reduced the risk and work factor by a lot!

The other big positive about doing this work in the Spangled Bedroom was that we were able to do it in front of our wonderful visitors!

Sarah and Lolly unpicking a

Sarah and Lolly making a temporary repair to the galloon edge.

We all enjoyed talking to our visitors about the work we were doing. It really allowed people the opportunity to see things that are so often hidden away behind closed doors. Here at Knole we are getting more and more excited about doing this kind of work in front of visitors as we really get going on building our brand new conservation studio! When the studio opens it will provide a unique experience for visitors so make sure you come to check it out in a few years.

The rich colours of the back of the tapestries gives a better idea of how bright and vibrant they would have looked when new.

The rich colours of the back of the tapestries gives a better idea of how bright and vibrant they would have looked when new.

We used special 'Musreum Vacuums' to carefully clean the surgace dirt from the front and back of the tapestries.

We used special ‘Musreum Vacuums’ to carefully clean the surgace dirt from the front and back of the tapestries.

Until then there’s plenty of interesting conservation works to be seen at Knole. Now that the Spangled Bedroom is providing more space you may just see more conservation projects appearing in the near future…

Knole Conservation Team

How do you wash your tapestries?

Three of the Spangled Bedroom tapestries that were prepared for washing back in November (Tapestrytastic!) safely made their way to Belgium. Siobhan our project conservator made the trip out to see the tapestries go through the washing process.

The De Wit Centre

De Wit Royal manufacturers, founded in 1889, have been restoring tapestries for over a century. At international level, it is one of the world’s leading restorers for museums and private customers. It has combined the use of traditional skills and state of the art conservation techniques to offer a facility that can deal with all aspects of tapestry conservation and restoration.

In the past tapestries were most commonly washed using temporary baths made from polythene and plastic pipes. It required large quantities of softened and deionised water as well as adequate drainage. The tapestry would be fully immersed in the bath and to facilitate efficient soil removal, mechanical action in the form of sponging was essential. In order for the whole surface of the tapestry to receive the same treatment, the tapestry would be rolled on a roller in the bath as the sponging progressed across its entire surface.

Though this method of washing is highly efficient at soil removal, there are drawbacks. The tapestry undergoes considerable physical stress as it is repeatedly rolled and rerolled. Mechanical action and sponging can damage fragile threads. The process is lengthy and drying can take between 12 and 24 hours allowing potentially fugitive dyes to migrate and spread.

Yvan Maes De Wit, the present director, represents the fourth generation of tapestry weavers and restorers at de Wit, and has been responsible for developing a unique system for tapestry washing using aerosol suction. This was patented in 1991 and is the only facility in the world that offers this service.

Diagram from the De Wit website showing the wet cleaning process.

Diagram from the De Wit website showing the wet cleaning process.

This system uses a combination of aerosol spray and vacuüm suction. It is fitted with integral sensors to control pH, temperature, water flow and pressure. The facility consists of an enclosed chamber with glass panels. The base is a large suction table 5 x 9 metres. Ranged across the ceiling are 45 aerosol sprays approximately 1.75 metres above the platform. During the cleaning process the tapestry is held in place by continuous suction. When the aerosol is turned on the chamber fills with water vapour which is drawn down evenly through the entire tapestry.

Start of the washing process

Start of the washing process.

A low concentration of a non-ionic detergent is introduced to the aerosol system for as long as is deemed necessary for soil removal. This is replaced by softened and then de-ionised water during the rinsing process. In cases of extreme soiling sponging can be carried out from a gantry. The tapestry is still held under suction whilst being sponged, therefore there is no possibility of movement which would result in damage to weak areas of silk.

The aerosol/suction combination creates a very even and intense cleaning system with the advantage of the entire tapestry being treated simultaneously. The continuous flow through the tapestry means dirt is loosened from the fibres efficiently and then immediately drawn away avoiding the danger of re-deposition. There is no movement of the tapestry, therefore no mechanical damage from manoeuvring a wet textile can occur. The tapestry is never completely immersed in water thus avoiding dimensional change or shrinkage.

The washing control room

The washing control room

Another good property of continuously working suction is that fabrics that have undergone previous deformation can recover their shape. Irregularities in the fabric can be flattened out when it is dry and immobilised, on the suction table, before cleaning begins. This latter operation together with drying enables the old fabric to recover its original shape.

Finally the full treatment time is quite short. A tapestry measuring 45 m² can be completely dried at 30° in two hours owing to the process of uninterrupted suction over the entire fabric at the same time. If we consider that average cleaning time lasts one hour and rinsing 2.5 hours, the whole cleaning process therefore requires less than 6 hours. Any risk of hydrolysis of fragile fibres is thereby averted and the entire treatment can be constantly supervised throughout a normal working day.

Washing the Spangled Bedroom Tapestries:

Two of the tapestries, one large and one small were laid out on foam to support them on top of the mesh layer of the large suction table. The tapestries were sprayed from the top of the wash chamber, with a mist of soft water and conservation detergent while the suction from beneath drew though the wash liquid.  A sample of the wash liquid is collected throughout the treatment and tested for pH and conductivity.

Sample of the wash water

Sample of the wash water being collected.

The dirt in the tapestries is very acidic, so as the wash progressed this improves and moves toward a more neutral PH. Conductivity measures the ability of a solution to carry a current, the very black dirty water coming off the tapestry at the start of the wash had a high conductivity. This improved as the wash progressed and the water passing through the tapestry became clearer, carrying less particles and ions that could carry a current.

A video microscope mounted on a boom shows the surface of the tapestry and any especially weak areas can be closely monitored. This process lasted for around an hour. It was clear during this process that where there was glue residue on the reverse the water could not be pulled though the tapestry effectively.

Animal glue removed from back of tapestry.

Animal glue removed from back of tapestry.

Once the aerosol spray was turned off the front of the wash chamber was opened and the two conservators from De Wit were able to start gently brushing the tapestries with soft brushes to help loosen and remove the dirt and adhesive. They started by turning off the suction and rolling the tapestry on a large pipe to its centre, this allowed them to spray and brush the reverse of the tapestry rolling back as they went.

Mechanical cleaning of front of tapestry

Mechanical cleaning of front of tapestry.

Mechanical cleaning of tapestry reverse

Mechanical cleaning of tapestry reverse

They then brushed the other half of the reverse in the same way. After they had finished brushing the reverse, the suction and the aerosol spray were turned on for ten minutes to draw through the loosened dirt. After this the aerosol spray was turned off and the front was brush washed, then again the aerosol spray was applied to wash through the loosened soiling. The water used is approximately 26-28 degrees and the warmth allows the animal glue to be softened and removed. This process lasted for about 1 hour.

Following this the tapestries were rinsed for two hours. As samples of the water were collected you could clearly see how the washing process and rinsing had removed the soot, dirt and acidity from each tapestry.

Samples of wash water

Samples of wash water

The suction remained on during the drying process. Very large towels were laid across the top of the tapestries, which were then covered with a thin plastic for about 30 seconds. This process was repeated twice with the towels and twice with absorbent paper to blot a lot of the water out of the tapestries.

Drying the tapestry.

Drying the tapestry.

They were then left to dry at 30 degrees with the suction on for two hours. The complete wash and dry cycle was finished by 7pm. It was then left to rest overnight in situ. The transformation of the tapestry after cleaning was amazing – not only were the colours considerably brighter, with unsightly glue stains removed, but the tapestry was soft and pliable to touch.

The tapestries after drying.

The tapestries after drying.

After drying 4 After drying 5 After drying



Conservation of the bed hanging linings from the Spangled Bed continued throughout last year. Here’s an update from the National Trust textile conservation studio:

Humidification and wet cleaning

 Humidification of linings

The linings and satin were laid out inside a humidity tent created from a metal frame (a strawberry cage!) with a polythene sheet over to enclose the lining. A humidifier was set up inside to pump a fine water spray into the tent.

Lining relaxing in a humidity tent.

The linings were allowed to reach a humidity of 95% to allow them to relax. As the object was starting to relax glass weights were applied and it was then allowed to dry flat. Humidification resulted in the linings and satin to regain some of their lustre and body.

Wet cleaning of linings

After testing a variety of methods, detergents and buffer solutions, each piece of lining was washed in the wash table, pinned out flat and left to dry.

 An IMS : Acetone : Water (40:40:20) mix was used at the beginning of the wash to remove greasy soiling, followed by a wash bath with Dehypon LS54 (a conservation grade detergent) without a buffer and also with a buffer with a pH of 6.

The linings had an initial pH of 3.2 and was very acidic, so by introducing these different wash baths and using a buffer, which is a means of holding the pH at a steady level, we allowed the pH to be increased slowly.

Applying detergent and sponging the silk damask lining.  The lining sits on a mesh covered grid in the wash table to allow the wash and rinse solution to drain away, preventing it becoming too soft.

Applying detergent and sponging the silk damask lining. The lining sits on a mesh covered grid in the wash table to allow the wash and rinse solution to drain away, preventing it becoming too soft.

The soiling is very bound within the fibres, probably due to acidity, and proved difficult to remove through wet cleaning. Some dye loss also occurred although prior to cleaning it was noted that the ground of the silk was ‘cloudy’ where the dye had run from the crimson into the cream areas. This was probably due to the high humidity which, in combination with historic atmospheric pollution at Knole, had caused the silk to become more acidic and de-stabilised the dye. There is still some greyness to the object with striations of grey but overall the lining has improved immensely.

left to right – samples of water collected during wet cleaning process.

left to right – samples of water collected during wet cleaning process.

Removal of the silk damask and satin patches

It was decided to remove the patches to allow a more effective treatment of the satin.  Any necessary conservation treatment would have been worked through the patches causing damage and the patches would be lost as a future resource for research.

 The satin patches and the damask patches on the reverse of the satin were found to be adhered with starch paste. Damp blotting paper was placed over the patch and weighted in position. It was left for several hours allowing the glue to swell and soften. The patch could then be peeled away from the satin.

Humidifying the satin patch with dampened blotting paper.

Humidifying the satin patch with dampened blotting paper.

The patches were easy to remove and fortunately most of the adhesive came away with the patch and was not left on the curtains. The aim is to document and conserve most of the patches which will provide valuable information on some of the textiles used to furnish Knole or Copt Hall during the late 17th century.
Once the satin was humidified and the adhesive softened, the satin patch could be peeled from the surface (above) and the patch removal complete  . Once the satin was humidified and the adhesive softened, the satin patch could be peeled from the surface (above) and the patch removal complete

Once the satin was humidified and the adhesive softened, the satin patch could be peeled from the surface (above left) and the patch removal complete (above right).

Once the patches were removed, the satin curtain panels were humidified using the same method as for the damask linings.

 Adhesive treatment of the linings

Once washed, the damask linings had regained some of their handle and were less fragile. However they were much split and required an even, all-over support but could not withstand extensive stitching. An adhesive support was selected as the most appropriate treatment. Fine silk crepeline, a very fine gauze-like fabric, was dyed to match the damask and the crepeline was stretched out on polythene (which makes a backing film) and a 25% solution in soft water of Lascaux adhesive, (360HV and 498HV in a 2: 1 ratio) was applied with a small roller. This creates a fine adhesive backed fabric.

The damask panels were laid out and aligned and small ‘plasters’ of crepeline were used to hold distorted areas in place. Panels of adhesive crepeline were cut to shape and then applied using a roller system and laying the film evenly on to the reverse of the damask. The panels were turned face up and loose fragments were re-positioned.

Applying the adhesive coated silk crepeline to the reverse of the lining using the roller system.  The polythene backing is peeled away during the process.

Applying the adhesive coated silk crepeline to the reverse of the lining using the roller system. The polythene backing is peeled away during the process.

The adhesive film was then activated using a heat suction table and once cool the adhesive was set and the silk fixed to the support. Both linings had to be activated in two parts as they were too wide for the table.

Fixing the film to the lining on the right hand side, part of the two part activation.

Fixing the film to the lining on the right hand side, part of the two part activation.

The final stages of the treatment of the linings are to apply a dyed silk support to the reverse and dyed conservation net overlay using support stitching. This will take place once the proper right curtain linings have reached the same stage.

Note: All images © NT Textile Conservation Studio