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!


Listening to the Furniture

At the beginning of March this year Knole was visited by Nigel Blades, the Preventive Conservation Advisor for the National Trust and a team of researchers from the Polish Academy of Sciences in Krakow. They were here to install some pioneering technology in the world of heritage sciences. With the help of furniture conservator John Hartley they have attached acoustic emission (AE) monitors to some of the most important objects in the house. The basic principal of these sensors is to listen for otherwise imperceptible noises emanating from objects as they react to the changing environment around them. 

Some of the sensors have been attached simply by wedging plastazote (an inert spongy material) into a convenient crevice, whereas others required gluing by a furniture conservator (although a hairdryer was needed to speed the drying process in the freezing temperatures at Knole!). Using a combination of gluing, wedging, and tying all of the monitors have been successfully attached.  

John Hartley preparing the sensor mount (left) and the finished sensor (right).


Sensor wedged with plastazote into a convenient gap in the 17th century Gole table.


These monitors are designed to pick up the tiniest cracks and pops emitted by the furniture as it reacts to the environment around it. The relative humidity (RH) in the Showrooms of Knole can cause certain materials such as wood and metal to expand and contract as it fluctuates. It is impossible to tell how much the objects themselves are moving with the naked eye and so this AE method has been developed to help us better understand what seasonal variations in RH are doing to our collection. The sounds the equipment are monitoring for are so tiny they couldn’t hope to be heard without these specialist sensors. 


The monitoring equipment in the Spangled  Bedroom


Sensors have been attached to 4 objects in the house; the Gole table and a torchere in the Great Store and the Jensen table and a torchere in the Spangled Bedroom. Selecting these objects allows the researchers to compare the effects on similar objects in varying conditions. The Spangled Bedroom currently has no environmental control at all. This means the the temperature and relative humidity change with the weather conditions outside with no human intervention. The Gole table in the Great Store however is subject to environmental control which keeps the relative humidity below 65% at all times. 


The full setup on the Jensen torchere in the Spangled Bedroom.


The ideal conditions for a mixed material collection in the National Trust is between 40% and 65% although this is not always possible. Part of our long term conservation project at Knole is to try and install environmental control throughout the Showrooms so that the RH can be carefully controlled.  


Every room has an environmental monitoring device like this. The Spangled Bedroom one has been placed behind the table and is recording temperature and RH every 15 minutes.


The AE project will run for a full year from now and it will allow us to understand and better manage the change from an uncontrolled to an RH-controlled collection. The sensors and laptops will be left in their current positions permanently and will be checked remotely from Poland once a week to make sure everything continues to function properly. 


Furniture conservator John Hartley (left) and researcher Marcin Strojecki (right) discuss the placement of an AE monitor on the Gole torchere.


It was fascinating to see researchers and conservators of different disciplines come together at Knole to put this project together. Hopefully it will yield some interesting results!


Thanks go to Nigel Blades and everyone on the AE project team for providing the information and pictures in this weeks blog.


What to do with wet and mouldy antlers?

The Knole collection does not have many natural history objects, apart from antlers.  Some, like those below, are quite small…

Antlers over the fireplace in the Brown Gallery.

…others are huge!

Irish Elk antlers that hang in the Loggia, found in a peat bog in the 18th Century. They are 10,000 years old!

The antlers from the Brown Gallery had temporarily been in store. Unfortunately where they were stored suffered from water ingress during the wild, wet and windy weather over Christmas.  The storage box they were in had collected a lot of dripping water.

This subsequently led to mould growth on the surface of the antlers.

As none of the antlers in the collection had become wet, or grown mould before, we weren’t sure what the best course of action was. So que an e-mail to the National Trust’s advisor on natural history Simon Moore.

Parts of the antlers were still very damp.

Simon’s advise was to dry any surface water off of them using paper towelling.  Then using a hogs hair brush, apply industrial methylated spirit to remove and neutralise any fungal growth.

Applying the methylated spirit.

After leaving methylated spirit on for about five minutes any excess fluid was removed with paper towelling.

Drying off excess methylated spirit.

Both antlers after methylated spirit treatment.

Then we needed to consider a suitable location to leave the antlers so they could dry out, but slowly.  If rapid drying was to occur this could have resulted in cracks and splits in the antlers. The relative humidity of the space chosen had to be between 50-55%.  So that meant there was only one room we could use, the Great Hall.  This is currently the only room in which we have consistent environmental control and could guarantee that the relative humidity would not get too high and potentially damage the antlers while they were drying out.

The antlers have been in the Brown Gallery since at least 1881, when this photograph was taken.

After two days drying out in the hall we inspected the antlers for any signs of active mould or the effects of drying out.  We’re pleased to say that the mould that had grown has gone with no evidence of new growth.  They have dried out nicely without incurring any damage.  We’ll update the object condition report to record the fact they got wet and grew mould and how we treated them and have them back on display for when the house re-opens on 8th March.

So now you know what to do should your antlers ever get wet and mouldy!

Alex, Emily, Lucy, Melinda, Sarah and Zena

Mould research continues

We currently have two research projects on mould at Knole.  The first is being carried out by students at  The Courtauld Institute of Art.  Below they provide us with an outline of their research:

Our project considers an 18 months environmental survey monitoring the daily and seasonal changes in temperature, humidity, light levels and airflow across a representational sample of the show rooms at Knole. The historic and listed building suffers from active mould damage which may be exacerbated by the uncontrolled environment with huge variations in temperature, humidity and light throughout the year. Mould damage is an on-going problem that has caused damage to paintings, textiles and furniture throughout the many rooms in Knole.

On-going to our environmental survey will be the sampling, culturing and identifying the of extant mould from the property. We aim to identify the currently active mould strains & their ideal living and growing conditions throughout the rooms being tested.

Petri dishes where mould has been culktured from the show rooms in agar jelly.  3 petri dishes were lpaced at different locations in the Spangled Dressing Room, 3 in the Leicester GAllery and Billiard Room, 2 in the Venitian Ambassadors Bedroom, and 1 in the Brown Gallery.

Petri dishes where mould has been cultured from the show rooms in agar jelly. Three petri dishes were placed at different locations in the Spangled Dressing Room, three in the Leicester Gallery and Billiard Room, two in the Venetian Ambassadors Bedroom, and one in the Brown Gallery.


A close up of some of the cultured mould!

Our intent is to use our data and environmental model to predict the efficacy of environmental controls and how these controls may inhibit or prevent the future growth of mould on the artworks in Knole. Our model will also facilitate making new recommendations to establish safer environmental control for the historically important and diverse collections. It is an exciting project that we are looking forward to completing.

photo 2

Students here are using a cotton wool swab to take a sample of mould from the surface of a painting in the Billiard Room.

The students also took a sample of mould from the Billiard Table baize.

The students also took a sample of mould from the Billiard Table baize.


Here an impactor air sampling machine is being used to take air samples from each of the show rooms the students are researching.

Impactor air samplers use a solid or adhesive medium, such as agar, for particle collection. In a typical impactor sampler air is drawn into a sampling head by a pump or fan and accelerated, usually through a perforated plate (sieve samplers), or through a narrow slit (slit samplers). This produces laminar air flow onto the collection surface, often a standard agar plate or contact plate filled with a suitable agar medium.

The velocity of the air is determined by the diameter of the holes in sieve samplers and the width of the slit in slit samplers. When the air hits the collection surface it makes a tangential change of direction and any suspended particles are thrown out by inertia, impacting onto the collection surface. When the correct volume of air has been passed through the sampling head, the agar plate can be removed and incubated directly without further treatment. After incubation, counting the number of visible colonies gives a direct quantitative estimate of the number of colony forming units in the sampled air.
This information was taken from the following website:

Our second research project is being undertaken by Tess Evans as part of her Masters in Museum Studies with Leicester University.  Her research project is investigating the use of a new biocide to remove mould from heritage objects and sites.  Tess currently has a trial
underway on a mould affected wall in a servant’s corridor off the Leicester Gallery.

mould LG1

Here is the wall before treatment.17.4.13

A frame has been placed against the wall and Tess has cleaned each square with a different concentration and method of application of the biocide. The idea is to monitor its effectiveness and how quick the mould returns and Tess will return at regular intervals to assess this and take photographic records.


Area 3 being cleaned with an impregnated wipe.


The sectioned area after cleaning 17.4.13

One of spare Hanwell temperature and relative humidity monitors has been placed in the corridor next to the trial area so that Tess can use the data to assist her research.  The monitor record an hourly average of the temperature and relative humidity 24 hours a day.


The same section on 3.6.13 with no mould growth evident! (sorry for the awful colour, my flash didn’t go off)


Area of wall with the frame removed to clearly show the cleaned area where no mould has regrown. 3.6.13

Thanks to Tess and the students from The Courtauld Institute of Art for the information on their projects.

Sarah, Lucy, Melinda, Zena and Emily

Textile cleaning in the Spangled Bedroom

Back in March, Jane Smith, one of the conservators from the National Trust’s Textile Studio in Norfolk came to Knole for 3 days to carry out some cleaning and preventive conservation to upholstered furniture in the Spangled Bedroom.


The X-framed chair and eight stools are covered with the same crimson satin as the Spangled Bed. It is decorated with an extremely rare applique strapwork pattern and originally sewn with small silver spangles, or sequins, now tarnished and viewed today as black dots.

The material is now extremely fragile due to the damage caused by light and relative humidity. Due to the importance and delicate condition of these textiles they are cleaned less frequently than some of the other textiles in the collection, and usually by a member of the Textile Studio team.


An area in the top right corner of the stool after vacuuming showing the removal of the build up of dust.

As well cleaning the textiles on the stools and chair with a conservation vacuum and a micro-vac on low suction, the chair had some netting applied to the back of the chair to prevent loose fibres and threads from coming away. Other parts of the chair had been previously netted a couple of years ago. The net is a mono filament nylon net dyed before hand in the studio to a special recipe to match the colour of the original material. Gutermann polyester thread is used to sew on the netting. Loose pieces of metal thread were also secured in place with bookbinder’s paste.


The netting is held in place with pins until it is secured with thread.

Jane in action!


Thanks to Jane for the photos and information from her report on her work. The Textile Studio have thier own blog to:

Emily, Lucy, Melinda, Zena and Sarah

Mould mould everywhere!

Of the 310 paintings at Knole at least 80 have some level of mould on the surface. Although mould is present or suspected in all rooms, the worst appears to be in the Spangled Dressing room, the Billiard room, the Leicester Gallery and the Reynolds Room and is a direct result of the very poor environmental conditions.

Mould on the surface of the painting 'Heraclitus' in the Billiard Room

Mould on the surface of the painting ‘Heraclitus’ in the Billiard Room

Mould penetrates the varnish and paint layers on paintings causing a white bloom on the surface, flaking paint and degradation of the canvas support. If left untreated this damage can become irreversible.

More mould on a portrait in Lady Betty's China Closet

More mould on a portrait in Lady Betty’s China Closet

In order to plan how we improve the environment in the showrooms in the future and how we can conserve the paintings, we need to better understand this mould growth; why it appears on some paintings and not others and in some rooms and not others; what factors influence its growth; how can we conserve the paintings and ensure the mould doesn’t return.

'Cimon and Iphigenia' bt Sir Peter Lely in the Spangled Dressing Room

‘Cimon and Iphigenia’ bt Sir Peter Lely in the Spangled Dressing Room

We have just started working with The Courtauld Institute of Art on a research project to investigate this mould problem. Six second year students are undertaking a full survey of environmental conditions in the showrooms, looking at data from the past and present to see how the current building works will affect the conditions.

Mould spores already growing in The Billiard Room...

Mould spores already growing in The Billiard Room…

...and in the Spangled Dressing Room, spores began to appear within 48 hours.

…and in the Spangled Dressing Room, spores began to appear within 48 hours.

The Petri dishes will collect mould spores that can then be analysed and identified. Samples have also been taken from the surface of some paintings and again will be analysed and identified. This project will run for 1 year.