Vacuum Table


Vacuum is used to wash paper for two reasons; firstly, by drawing water through the paper, substances can be removed which, otherwise, would remain in the paper; secondly, the vacuum stops the spread of the water allowing the conservator to wash close to an image that is fugitive in water.


When treating works of art on paper on a vacuum table there should be a layer between the object and the vacuum surface. Its primary function is to receive solvent and solute which are flowing out of the paper. A secondary function may be to act as a carrier for paper that has no wet strength. The usual carrier is blotting paper but it has its disadvantages;

blotter has no wet strength,

when water wets blotter the fibres swell which obstruct the passage of the water and wastes some of the vacuum,

blotter has disparate properties of expansion and contraction with changes of its moisture content when compared with most primary supports of works of art on paper.

I use four layers of ordinary cotton sheet because;

when wet the fibres swell but do not obstruct the passage of water,

its characteristics of expansion and contraction with changes in its moisture content are more in harmony with most primary supports,

it is re-usable.

The treatment carrier should always extend beyond the limits of the object being treated. If the conservator is worried that the object being treated will be difficult to pick up when wet she/he should insert a piece of the thick Bondina or the thick Hollytex, slightly bigger than the object, beneath it. This in no way interferes with the washing process.


humidify the object to be washed using your studio’s common practice erring on the high side,

humidify the cotton sheet by spraying on water and brushing the sheet with the flat of one’s hand away from the middle so moving wrinkles to the edge and beyond. With four sheets of cotton it seems to suffice to spray and flatten the top and bottom sheets only,

put the cotton sheet on the vacuum table with the object, recto up, on top of it,

cover the object and cotton sheet with clear plastic sheet.


The greatest potential loss of vacuum associated with the vacuum surface is at the join between the surface itself and the edge of the structure that contains it. The operator must ensure that the mask is of material thick enough not to get drawn into this slot and the operator must also ensure that there is clean contact between the mask and the surrounding horizontal area of the structure. Thereafter, those areas of the vacuum surface not covered by the object must be masked off. The mask should cover the object’s edges. Humidified paper dries out very fast and so, having placed the humidified object on the humidified treatment carrier on the vacuum table I cover all with an impermeable layer, usually clear, thin plastic sheet and I do the masking off beneath it.


There is a relief valve entitled ‘Vacuum Fine Control’ that lets air into the system by a route that does not go through the object and the vacuum surface. This should be open.

There is a lever labelled ‘Vacuum Coarse Control’ that closes the duct between the vacuum surface and the pump. This should be closed.

Remove the sheet covering the object and the masking and switch on Pump 1. Very carefully open the valve labelled Vacuum Coarse Control’; this allows air to flow from the vacuum surface to the pump. The moment the operator is aware air is flowing he/she must flatten any undulations in the object and the treatment carrier by;

brushing the object by hand so moving the undulation to the edge,

laying onto the object a piece of Melinex and brushing this to move the undulation to the edge; care has to be taken that the Melinex is small enough not to mask off too much and so raise the vacuum level which would increase the danger of creasing,

if all is in order then the airflow should be increased with further brushing as necessary,

if a crease looks likely the machine should be switched off and the process started again.

This process continues until the vacuum is full on and the valve letting air in is closed. Then switch the machine to Pumps 1 and 2.


There are papers used for primary support through which water will not go; new tracing paper for example or other heavily sized or coated papers. To some extent this does depend on the strength of the vacuum available but generally water can be coaxed through.

First test; mask off the object to leave an area of, roughly, 100mm X 100mm. With a watercolour brush put a drop of water on its surface. If this is drawn through in, say, one minute the test is positive,

second test; if the first test is negative either with a watercolour brush or a small hand sprayer increase the wetted area to some 75mm X 75mm within the window but making sure that no free water touches the edge of the mask ( this causes water to shoot under the mask into unwanted areas). If this allows the water to be drawn through again the test is positive,

third test; if the second test is negative repeat the first test using 50/50 IMS/water,

fourth test; if the third test is negative repeat the second test with 50/50 IMS/water,

fifth test; if the fourth test fails repeat the second test using 50/50 IMS/water with a modicum of Synperonic A7,

if this test fails it must be accepted that water will not, safely, go through that particular paper and hopes of washing it must be abandoned. If, however, it does go through the conservator should then test the wetted area of this test using 50/50 IMS/water to ensure that the Synperonic A7 can be washed out.


Let it be assumed that water, without any additives, can be drawn through the paper to be treated. This is nearer to actuality than it first appears because, once water with additives has gone through, frequently water without also goes through. The conservator is now free to spray the object, or to apply water in other ways, over the whole exposed area. It is generally found that the water goes through faster in some places than others because of image, acid attack, mould damage to the paper’s sizing, et cetera. Frequently there are areas where there is free liquid on the surface and it is disappearing only slowly. Downflow can be maintained or speeded up by continually spraying the more porous areas thus making the vacuum work harder. If, conversely, water passes though the paper easily this might be described as a conservator’s win win situation because the spread of the water is controlled by the available vacuum. The conservator will realize that the treatment carrier cannot hold the volume of water being applied to the object which means that free liquid is going into the machine. This does not matter because the machines are designed to cope with this; nor does it obviate the use of the treatment carrier because the carrier filters out a lot of the dirt.


In this initial penetration of the paper by water there may be areas which the conservator will want to keep dry. I cut out a mask of thin Melinex that just covers such an area and another mask of blotter that is bigger. The size of the blotter depends on the porosity of the paper; the slower the flow of the water through the paper the bigger the blotter. It is to stop free liquid from touching the join of the edge of the Melinex and the object. Once most of the washing is done

the area between the edges of blotter and Melinex can be washed with water applied by a watercolour brush or, perhaps, by a small hand sprayer. If the paper holds a lot of the products of degradation such washing sometimes leaves tidemarks on the verso and, if the paper’s sizing has been damaged by small circles of mould or foxing, also on the recto. The only partial remedy for this that I have found is, at the end of the treatment on vacuum, to place the object in a humidifying chamber that has small quantities of water vapour in it. This sometimes allows the object’s humidity to even out which disperses the tidemark.


The inclusion of synperonic A7 in the wash water (3mg /L) can have a good effect on the result of washing on vacuum but it must be rinsed out afterwards.


If there are areas of the object which have been kept dry during washing it is sensible to dry the rest of the object enough to stop water from flowing within the paper before turning off the vacuum.


The previous chapter, washing paper on vacuum, applies to bleaching in as much as it is required to prepare the object and treatment carrier, to get them onto the vacuum table with the vacuum on, to mask off as necessary and to get them off the table again when the process is finished.

Bleaching, it has to be admitted, is cosmetic. That the bleach does not benefit the physical properties of the paper is also conceded. It can be argued, however, that bleaching can improve the appearance of a work of art on paper so that the owner, guardian for the time being, curator, will pay it the respect needed to ensure its proper care and attention in its future.

Research is required to compare the harm to the physical properties of paper with and without vacuum. The differences between vacuum and immersion are; firstly, the conservator can guarantee that there are no residues left behind after treatment on vacuum; secondly, bleaching on vacuum often only affects the recto and the verso appears to be untreated or as discoloured as it was before treatment started; thirdly, if it is accepted that damage to the paper fibres is proportional to the strength of the bleach, the conservator has the opportunity to use a much weaker solution many more times on vacuum than in immersion and; fourthly, on vacuum the conservator can restrict attention to the discoloured areas of the object.

Conservators intending to bleach on vacuum should familiarise themselves with current research and I would draw their attention to the findings of Helen Burgess mentioned below:

Burgess, Helen D.

Practical considerations for conservation bleaching.

IIC-CG journal Vol 13 pps 11-26.

Burgess Helen D.

The use of chelating agents in conservation treatments.

The Paper Conservator vol 15 1991 pps 36-44.

There are others which can add to the fund of knowledge of the subject. These two papers are very readable. When discussing the preparation of solutions in the second paper mentioned above (heading 3, p 40) she says ‘Various methods can be used to prepare the EDTA solution. An easy one would be to start with the di-sodium salt.......’.

We turn now to a comparison of generally available bleaches for conservation. The views I express below are personal to me and my observations are restricted to bleaching on vacuum and may be at odds with the findings of others especially if their views refer to bleaching by other methods. I restrict the bleaches that I use to the following three; hydrogen peroxide, sodium di-thionite/EDTA and calcium hypochlorite. Let us discuss them seriatim;

Hydrogen peroxide; an oxidising bleach; I use a three per cent solution, the pH adjusted to 9 using calcium hydroxide. The bleaching action occurs when the solution is drying. It is, at best, a mild bleach. It will increase the brightness of paper a notch or two. A test using the solution soon establishes whether it is effective on a particular stain and, if not completely so, its use should be abandoned because the conservator would not wish to generate oxygen within the paper’s fibres to no advantage.

Sodium di-thionite/EDTA; a reduction bleach. I follow the advice of Helen Burgess in her second paper listed above making up a 0.1 molar solution of EDTA and a 2% w/v sodium di-thionite solution, I mix them and adjust the final solution to pH 8.0 using sodium hydroxide. I use this specifically for the reduction of ferric and cupric oxides to ferrous and cuprous oxides so that they become soluble in water and can be washed out. This can be used as a general bleach but its efficacy beyond the chelation of metal oxides is limited. Having established that the stain being treated is not a metal inclusion I abandon this bleach in favour of calcium hypochlorite. This is because I suspect that sodium di-thionite/EDTA will be only partially successful as a general bleach, there can be colour reversion and, to guard against it, one waits for an hour and repeats the treatment if necessary and there can still be colour reversion up to one year later. Coupled to that the bleach can leave a slightly yellow hue. In its favour it must be said that if the metal is left in the artefact the paper in the presence of any moisture will eventually rot away and so its use in this context is, without question, of benefit.

Calcium hypochlorite; an oxidising bleach. I mix a 1% solution (10g/L). After it has settled and cleared I filter it and then dilute it one part 1% solution to 3 parts tap water which gives a 1/4% solution or 1 part 1% to 2 parts tap water which gives a 1/3% solution. I then adjust the mixture’s pH to 9.0 with citric acid. If there are small prominent stains in the object I may use a 1% solution (pH adjusted to 9.0); I never use a more concentrated solution. I always use either 1/4% or 1/3% for overall bleaching and vary the number of applications to suit the condition.


My studio is in west London and the tap water there is pH 7.9 to 8.0. It has been naturally filtered through the chalk beds of the north Downs and its alkalinity is largely from calcium. I use tap water in testing the porosity of the paper under treatment and for washing the object prior to bleaching. If the tap water were not alkaline and rich in calcium I would use a solution of calcium hydroxide to wash the object prior to bleaching. This washing has three functions; the first is to wash away the products of degradation; the second is to de-acidify the object and the third to ameliorate or dilute the first applications of bleach giving the conservator the opportunity to observe the bleaching action before it reaches full strength. I apply this rule to any area to be bleached however small. It is sometimes hard to judge the effect the bleach is having and the conservator should err on the side of caution by rinsing the object with an alkaline solution to de-nature the bleach and then drying it to ensure the object is not over-bleached. As a guide to the end result to be sought I use the maxim; ‘when the treatment is complete the artefact should look its age but should appear well kept’. The conservator may have to approach this final condition by several stages. If the bleaching is of spots or of discrete areas the result sought is uniformity. If there is then to be a general bleaching the conservator should bleach the small areas and achieve uniformity before carrying out the overall bleaching.

It is necessary to de-acidify the object at the end of the bleaching process using an oxidising agent in order to convert any remaining carbonyl groups into calcium salts; again, I use west London tap water.

To apply the bleach I use a watercolour brush of man made fibres of a size that suits the size of the stain or foxmark down to a double o brush for small foxmarks. The conservator should, initially, keep the bleach well within the stained area because its tendency is to spread by mixing with the water in the paper’s fibres and by over-sized droplets both of which can cause a halo outside the perimeter of the stain. For larger stains and for overall bleaching I use hand sprayers of the type one can buy at garden centres or better ones which are made for the hair dressing industry. Boots the chemist sell a small hand sprayer of, say, 50mL capacity. Muji sell a better one of the same size. When applying the bleach with these sprayers it is wise to have a spare one because, sometimes, they block.


Traditional repairs on vacuum have advantages over such repairs without vacuum in matters of accuracy and speed. The vacuum, particularly with the light box beneath, allows accuracy of alignment, easy application of adhesive and repair tissue and drying the repair flat. If an artefact is very fragile and has broken into pieces the conservator can repair it on an inert layer ( I use the thick Bondina) on vacuum, verso up, turn it over so that the repair tissues are on the underside and the object is on the inert layer recto up. It can then be de-acidified, washed, bleached and dried. Care must be taken with drying; if over-dried stresses develop. It can, however, be lifted on its Bondina and put in the press while it is still damp or left to air dry. The adhesive re-constitutes itself as it dries.


A useful description of the mechanics of pulp repairs is given in an excellent paper entitled

‘leaf casting with dermal tissue preparations: a new method for repairing fragile parchment, and its application to codex Eyckensis’ by Jan Wouters, An Peckstadt and Lieve Watteew. The Paper Conservator vol 19 1995 pps 14 to 18. A keen eye will see where the idea of a light box beneath the vacuum surface comes from. Comments on methods of application and masking off are to be found in the third year project of the Camberwell BA course 2000-2003 by Ben Buchanan.

I use the following fibres for pulp repairs:

new cotton linters

Jap repair tissue cut into small pieces

fibres of a degraded rag paper as a colourant

coloured papers from art shops where the dye is stable in water as a colourant

I have not found it possible to add colour to the pulp because it stains the parent paper. Swatches should be made to vary the ingredients to give the required colour match. No additives to the pulp are needed such as adhesives; the end result is surprisingly strong. Referring to the Codex Eyckensis paper, their system of masking off is to place Melinex on the vacuum surface with a hole cut in it which is just bigger than the area of the pulp repair. Then to cover the Melinex with Hollytex or Bondina also covering the hole. Then to place the object on the Hollytex or Bondina. The edge of the hole in the Melinex can be outlined with an ink not soluble in water to make it visible with the light box switched on. Their problem was that the parchment pulp was difficult to remove from whatever was immediately beneath it and they did not wish it to stick to the vacuum surface. Paper pulp does not behave in the same way and the operator may, if so desired, drop the pulp in suspension straight onto the vacuum surface. Either I do this or I put a thick Bondina onto the vacuum surface if the object is weak and in need of further support for removal. The repair should always be dried before removal from the table and the thick Bondina makes this process quicker. It will be noted that water is going straight into the machine. It is, however, clean and gets caught in the free liquid traps. When these traps are full the floating ball blocks access to the vacuum pump. The operator should check these and empty them if necessary to ensure that the vacuum is not removed at a critical juncture. The mixture of pulp in water should be very thin, or little pulp in lots of water. The conservator can use a variety of containers to hold the mixture and to drop it into place such as pipettes but the best I have come across was given to me by a Parisian conservator, Silvia Brunetti, who did the most beautiful repair with it. It is manufactured to remove mucus from babies’ nostrils and is available at most chemists. It has a white rubber bulb and a clear plastic nozzle with a comparatively wide aperture at the end of 2.5 mm which allows for an even distribution of pulp. Silvia Brunetti advises that one always needs more pulp than one thinks. The repair should be dried before removal and any tendency to stick is eased with a palette knife inserted beneath the repair.


Solvent based adhesives have been around for a long time. The early ones (1845 according to the AIC Tape Removal Handbook) were rubber based. The synthetic adhesives arrived in the late 1950’s and from then there was a surge in their use with no consideration as to the future damage they would cause.

The actual removal of the adhesive from the fibres of the paper I do only on vacuum. Whether the vacuum alters the action of a solvent on an adhesive is not clear to me but what follows is from my observations and may be at odds with the findings of others.

I list below the type of adhesive and the solvent that dissolves it on vacuum:

new brand clear and frosted tapes: petroleum spirit

Sellotape: acetone

Sellotape: acetone and toluene either mixed or one after the other

Sellotape: toluene

masking tape: toluene

masking tape: acetone

Uhu: dichloromethane

Cow Gum: dichloromethane

there are adhesives which dissolve in 1:1:1 trichloroethane.

dichloromethane is highly toxic and should only be used with a fume hood.


Sometimes the carrier of the adhesive is long gone. Sometimes it falls off or can be peeled off. If it is still on and the conservator does not intend to work on it immediately then it should be left in place. In removing the carrier it is, perhaps, best not to force the adhesive into the paper. The following are some methods of carrier removal:

insinuate the solvent between the carrier and the adhesive with a small brush (I use watercolour brushes with man made fibres). The disadvantage of this method is that the solvent carries dissolved adhesive off into the object and deposits it there:

insinuate the solvent between the carrier and the adhesive with a small brush on the vacuum table. The advantage of this method is that the flow of the solvent is contained because when it flows beyond the adhesive it is drawn through the object. But this does not always work:

apply steam from a steam pencil to the carrier. This softens and swells the adhesive which allows the carrier to be peeled off. Sometimes this also does not work:

run a heated spatula along the carrier. This forces the adhesive into the paper which might not help:

apply the adhesive’s solvent to the back of the paper which can break the bond between carrier and adhesive. This works well with thin papers and tissues. With thicker papers adhesive is carried off into the object:

apply the adhesive’s solvent to the back of the paper on vacuum. Again, this does not always work because the solvent evaporates before the object can be taken off, turned over and the carrier lifted.


So long as the vacuum is strong enough to give the operator reasonable control over the spread of the solvent one should not be too namby pamby in the application of the solvent to the adhesive. I generally use a flat watercolour brush with bristles of man made fibres of a width of 8 to 10 mm. I fill the brush and plant a drop or blob onto the adhesive rather than paint it on. I then watch its disappearance to see how long it takes and how far it spreads. If the drop is repeatedly planted in the same place the speed of its disappearance should increase if it is dissolving the adhesive. If it disappears too quickly so that there is not time for it to do its work, the vacuum should be reduced to increase what might be termed ‘Dwell Time’; the time it remains in sight.

If the operator wishes to stop work for any reason the solvent should be allowed to dry or should be dried with a hair drier before turning off the vacuum just so that it does not spread sideways when vacuum is removed.