University's Workshops

University's workshops

Lok-Hang WAN

Workshop 1, Northumbria University

Colour matching and in-painting techniques

1 Introduction

Tratteggio (rigatino) is an in-painting method that applies groups of straight lines to fill the lacunae in a painting. The lines form a colour pattern that merges the missing paint with the original when viewed from a distance but is distinguishable in a close look. Delicate layers of lines should be put successively to form a steady colour 1 .

In this workshop, the processes and materials used for inpainting are introduced and examined. The manual skills in preparing paint media and application of in-painting are developed.

Characteristics of different common pigments, such as transparency, will also be discussed.

2 Materials

2.1 Materials, solvents and reagents

• A box of dry powder pigments with 20 colour (synthetic)

• Solvent: De-ionised water

• Binding medium: egg yolk

2.2 Tools, equipment and instruments

• A range of sable brushes (No.2/0, No.0, No. 1)

• Palette and palette knife

(Above) Fig 1. Pigment set; (Left) Fig 2. Tools used in the tratteggio in-painting

3.1 Egg tempera medium preparation

• Break the hen’s egg and separate the egg yolk

• Pinch off the vitelline membrane and collect the yolk content

• Add a few amounts of water to decrease the greasiness of the yolk2

• Stir well to a liquid

3.2 Pigments application

• Use the tratteggio (rigatino) method to build up layers of inpainting

• Combine each pigment with the egg tempera medium separately

• Paint the paints to boxes in the replicated ground layers with different colour groups

• The upper half box is the sample of one thin layer, and the lower half is the multilayer part that is the opaquest can get from that pigment

3 Methodology

Fig 3. Applying in-painting in the sample canvas

Fig 4-6. Mixing pigment powder with egg binder and water by palette knife and brushes

4 Result

Please see the pigment characteristic research in Appendix. The tested canvas and the characteristic of egg tempera and pigments are recorded:

Fig 7. in-painting canvas of 20 pigment colours by tratteggio method

Egg tempera is a fast-drying medium that allows pigments to dry quickly and hence can apply multiple layers of trateggio in a short time. Although different pigments have different hydrophilicity toward the egg binder, the egg tempera is overall easy to handle.

Considering the process of pigment-binder mixing, ochre colours and some of the pigments are hydrophobic and therefore difficult to mix with the binder. For example, lamp black, van Dyck brown, and alizarin crimson dark repel when water and egg binder are added. Green earth light is also slightly hydrophobic, so these pigments require less water solvent and binder when mixed. The high pigment load results in opaquer colour even by only applying one layer of in-painting.

In general, transparent colour has a low hiding power than opaque colours. Hiding power can be defined by the refractive index of the pigment. For example, Titanium white (rutile form) has the highest refractive index (2.72) among the whites, which is also the opaquest white pigment. 4 On the other hand, Prussian blue has a refractive index of 1.56, making it a transparent blue pigment 5 .

Darker ground layers are more difficult to hide by the pigments. In the dark red ground layer column, the ground colour

Footnotes

1 Grenda, Magdalena. 2010. ‘Tratteggio Retouch and Its Derivatives as an Image Reintegration Solution in the Process of Restoration’, EGG-2010 - Horizons, 1.1<https://journals.openedition.org/ ceroart/1700#citedby>

2 Gettens, R. J., and G. L. Stout. 2012. Painting Materials: A Short Encyclopedia (Dover Publications),p.19

3 Fitzhugh, Elisabeth West (ed.). 1997. Artists’ Pigments: V.3: A Handbook of Their History and Characteristics (Washington, D.C., DC, USA: National Gallery of Art, OUP), p.295

4 Fitzhugh, p.308

5 Fitzhugh, p.197

is shown even in the opaquest triangular region. Transparent colours such as Prussian blue, Indian yellow, Alizarin Crimson dark, van Dyck brown and raw umber, the hue in the very transparent area, are barely seen.

Moreover, different ground colours result in various tones of the same pigment. Pigments on the darker ground layers have a less bright appearance than on lighter ground layers. For instance, Prussian blue looks nearly black on the dark red ground layer but looks like a dark blue with greenish colour on the yellow ground layer. This effect is less obvious in some high opaque pigments, such as cadmium pigments and other metal pigments.

To summarize, the tratteggio method of in-painting can show a difference in close look but merge with the rest of the painting when viewed from a distance. It helps to classify which part of the painting has conservation work and what others are the original work. Due to differences in the hiding power, pigments used in in-painting may be affected by the colour of the ground layer, with the darker the higher effect. Research should be done before applying in-painting to any conservation work to achieve the best colour matching with the background.

Bibilography

Baty, Patrick. 2017. The Anatomy of Colour: The Story of Heritage Paints and Pigments (London: Thames & Hudson)

Berrie, Barbara Hepburn, 2007. Artists’ Pigments: Vol. 4: A Handbook of Their History and Characteristics (London: Archetype Publications)

Gooch, Jan W. 2011.Encyclopedic Dictionary of Polymers, 2007, (New York, NY: Springer New York) Fitzhugh, Elisabeth West. 1997. Artists’ Pigments: V.3: A Handbook of Their History and Characteristics (Washington, D.C., DC, USA: National Gallery of Art, OUP)

Gettens, R. J., and G. L. Stout. 2012. Painting Materials: A Short Encyclopedia, Dover Publications Grenda, Magdalena. 2010. ‘Tratteggio Retouch and Its Derivatives as an Image Reintegration Solution in the Process of Restoration’, EGG-2010 - Horizons, 1.1

Rose, J., 2022. Pigments and their Chemical and Artistic Properties. [online] Jcsparks.com. Available at: <http:// www.jcsparks.com/painted/pigment-chem.html> [Accessed 10 October 2021].

Roy, A., 2012. Artists' pigments. Washington: National Gallery of Art. Roy, A. 2012. Artists’ Pigments: Vol. 2. Washington: National Gallery of Art.

Toch, Maximilian. 2012. Paint, Paintings and Restoration (Literary Licensing)

Workshop 2, Northumbria University

Surface cleaning - Verso

1 Introduction

Cleaning verso is a vital process in the conservation of easel paintings as surface dirt tends to speed up the deterioration of the materials. Proper cleaning can prevent the artwork from further damage. Meanwhile, improper cleaning or over-cleaning may remove unwanted materials such as flake paints on recto or marks on verso, causing further damage. Therefore, choosing proper cleaning materials and methods is extremely important.

The choice of the cleaning material should be inert, non-abrasive, does not leave any residues, and, most importantly, effective. However, no one material suits all

situations and has all the benefits without disadvantages. For example, suppose the painting is too fragile. A material that applies less pressure may be considered, even if it may not be the most effective cleaning agent.

Different cleaning materials are tested in this workshop on the same aged linen canvas with pencil marks, chalk marks and canvas stamp samples. The tested materials range from traditional to modern and from non-abrasive to penetrative. After that, the best method from the tested result will be applied to a real old oil painting.

Pic 1. Sample painting being half-clean (upper part)

Smoke sponge

Block eraser

Groom stick®

2 Materials

Pic. 2 Materials used in verso cleaning

Feather

Brush

Granted eraser

Drafted cleaning powder

3 Methodology

3.1 Dirt coated sample

• A sample of a linen canvas with dirt coated

• With marks of pencil, chalk and ink stamp

Pic. 3 Working on dirt coated sample

3.2 Sample testing

• Carefully remove dirt from the verso in a horizontal line and avoid removing any marks from the sample

• Mark the observation and handling properties of the cleaning method.

• Repeat the steps with all other cleaning methods

3.3 Verso cleaning of a real oil painting

• Clear the dirt behind the stretcher bars with feather and palette knife

• The verso was tested with six cleaning materials in six divided small area

• Choose one best suit material to clean half of the verso

Pic. 4 (above)

Keys removed before verso cleaning

Pic. 5 (left top)

Sample testing by a scapel

Pic. 6 (left middle)

Keys removing by hammer and clamp

Pic. 7 (left bottom)

Dirt clearing with a feather behind the strecher bar

Dry brush + vacuum

Feather

Smoke sponge

4 Result

Eraser (Block)

Eraser (Grated)

Draft cleaning powder

Groomstick®

Scalpel scraping

Pic. 8 Result of dirt coated sample

Smoke sponge

Draft cleaning powder

Groomstick®

Eraser (Grated)

Eraser (Block)

Dry brush + Vacuum

Pic. 9 Test result of different cleaning method on the real painting verso, the block eraser has been chosen to clean half of the canvas because it is the most effective materials in the cleaning test for this painting.

Pic. 10 Before cleaning, verso of the provided oil painting

Please see the appendix for the observations of different cleaning method.

Pic. 11 After cleaning of the half canvas, verso of the provided oil painting

5 Discussion

Generally, the smoke sponge is the best among the tested materials. It is because it can remove dirt effectively and cause low abrasions and leave no residues. Groomstick also shares the same advantages. However, it is not easy to handle as a smoke sponge. Compared with a groomstick, a smoke sponge is not that sticky and thus does not stick to the hands. When using the groomstick, especially when removing the top dirtied layer or reshaping it, it usually sticks on the hands or gloves.

High abrasive materials clean the surface effectively but may damage the painting. Block eraser and scalper may cause damage to the weave of the canvas easily, and applying large force may even cause damage to the recto and the paint film. However, in a small specific region like the edges of a mark or stamp, a block eraser or a scalper can provide precise cleaning and not touch the sensitive, important marks.

Suppose the verso is very delicate and cannot exert any external force. In that case, a low abrasion method can be used.

Bibilography

A dry brush with vacuum and feather cleaning is good for a sensitive surface as they apply only mild pressure. Yet, the effect of cleaning is also limited. In consideration of art conservation, protecting the object is always the highest priority.

The grated eraser and the draft cleaning powder can moderately clean the dirt on the verso. The biggest issue with using these powdered materials is that they leave residues on the verso. Powdered form materials can clean evenly on the object, but it may be difficult to remove all residues. Both eraser and draft cleaning powder have an affinity to fabric materials. Some tiny particles may be trapped in the gaps of the weave and speed up the deterioration of the object. To summarize, no material is best suited to all situations.

If a material is powerful in cleaning, it usually applies more pressure on the surface. In contrast, if the material is not effective in cleaning, however, it may provide a safe way to clean fragile materials

Nicolaus, K., 2006. The restoration of paintings. Köln: Könemann.

Stoner, J. and Rushfield, R., 2012. Conservation of easel paintings. 2nd ed.

Workshop 3.1, Northumbria University

Pre-consolidation

Moisture & Heat Sensitivity Tests

1 Introduction

This workshop uses my painting to understand the sensitivity of old oil paintings towards moisture, temperature, and the combination of two. Incorrect relative humidity and high storage temperature are usually the cause of

blanching, a kind of deterioration that occurs on the paint or the varnish layer of a painting. It presents by increased sheen or matt, softening the paint, or flattening of brushwork or impasto1.

2 Methodology

2.1 Moisture tests

• An area not on the edge of the recto was selected.

• The area was first tested using small dampened swabs of deionised water.

• Small dampened blotting paper square was placed over the selected area, followed by a small square of polyester film Melinex®

• Leave it for 1 minute. If there was no observable change on the surface, increase testing time gradually until blanching occurs, or up to 10 minutes.

2.2 Heat tests

• A discreet area of dark paint was selected. The surface was protected with silicone release paper

• Gently ironed over an area of about 1cm² and at a temperature of 40° C for 30 seconds initially and then extending to 1 minute.

• The temperature was increased in increments until reaching 75° C. Stop if there was negative change.

3 Result

2.3 Combined heat and moisture tests

• Combined the heat and moisture tests on a non-edge area. The area is first placed by a dampen blotting paper as prepared in part 3.1, followed by a Melinex® film.

• The area is heated with a heating spatula with gradually increasing temperature like part 3.2.

• No observable change in seperate moisture test and heat test

• Blanching occurs in 40°C after 3 minutes in the combined test

4 Discussion

Blanching is a complicated process that is affected by many factors. The whitening of the layer can be free fatty acids, metal soaps, waxes or their degradation products. Although the chemical content differs, moisture and high temperatures speed up the deterioration process.

The tested painting has no actual varnish layer. Instead, there is a thin layer of yellow hue paint. Besides the aesthetic function, varnish usually acts as a protection layer of the painting. Lacking varnish layer results in the paint layer being so

(Discussion cont')

sensitive to moisture and temperature. The dark green undergrowth region is chosen to be tested in both the heating and the combined test. A dark part can indicate adverse responses more obviously than lighter pigments. The dark green paint film has covered a large area of the whole painting with nearly 50% of the painting. This area can highly represent the limit of not deteriorating upon heat and moisture.

For oil painting, relative humidity has a larger impact on deterioration than high temperatures 2 . However, fluctuations in temperature always contribute to changes in relative humidity. In the combination of

moisture and heat, we can see that the mix of heat with moisture has an exponential effect on deterioration. The individual test for moisture and heat didn’t result in any permanent changes on the surface, even to the testing limit of 10 minutes. In contrast, the tested regions started blanching after 3 minutes at 40 °C in the combination test.

In the future conservation of the painting, it is suggested not to use water-based adhesives that require warming up upon use. For example, isinglass requires to heat up to 40 degrees while using, which may tends to blanch the painting surface.

Workshop 3.2, Northumbria University

Consolidation approaches to laying loose and flaking paint

1 Introduction

In this workshop, different types of adhesives are tested on a sample of flake paints on a cloth.

The properties and characteristics of the adhesives are observed and marked in a table of result. The low-pressure plate is also used on a sample painting on canvas.

2.1. Adhesives and reagents

• Isinglass (1%, 5%, 10%)

• Gelatine (1%, 5%, 10%)

• Aquazol 500 (1%, 5%, 10%)

• Jade 403N (50%, 70%, 100%)

• De-ionized water

2 Materials

2.2. Tools, equipment and _____ instruments

• Baby bottle warmer

• Acid free tissue squares 1cm² (for absorbing excess moisture)

• Sable brushes (size 0 & 1)

• Heated spatula

3.1 Consolidation of fragile flaking paint sample

• The tested adhesives were run in individual concentrations along the vulnerable cracks or flakes.

• Small squares of tissue were placed over the area to mop up excess moisture if necessary

• The sample was left overnight to allow moisture to penetrate through the layers and dry out.

• A piece of release paper was placed over the area for gently ironing with heat spatula

2.3. Using low-pressure plate

• Melinex 12 micron

• Blotting paper

• Sable brushes

• Heated spatula

• Adhesive: Isinglass

3 Methodology

3.2 Familiarisation with the lowpressure plate

• The plate was adjusted to the right height to suit the painting.

• A piece of Reemay ® paper, an acid free randomspunbonded 100% polyester paper, was placed on the plate to reduce the pressure exerted on the painting

• A silicone release paper was placed on the Reemay paper® to prevent sticking on the painting.

• The flaking area of the painting was placed on the silicone release paper

• A Melinex sheet covered the whole metal plate with a cut square opening for the consolidate area.

• Set the pressure to 40mB and turned on the pressure table.

• Isinglass was added around the edges of the flakes or cracks and ran down quickly by the pressure

Isinglass Jade

Best concentration for adhesion

• Isinglass (1%, 5%, 10%)

• Gelatine (1%, 5%, 10%)

• Aquazol 500 (1%, 5%, 10%)

• Jade 403N (50%, 70%, 100%)

Above:

Orginal sample with tested adhesives and concentrations marked

Below:

Net photo of result sample cloth

No one suits all, materials have various properties, and they favour different situations.

Higher concentrations usually mean giving a better adhesion strength. However, it also results in increased viscosity. For example, 10% Auazol 500 seems to have the highest adhesion strength; it did not penetrate the cracks well. On the other hand, 5% of the solution can consolidate and penetrate the layer.

Aquazol is the most favoured in the sample cloth among the tested adhesives. Nowadays, Aquazol is used in many functions such as adhesives, inpainting media, and even filling materials. It has so many benefits, such as good lightfastness, thermostability, and reversibility upon heating. It also has a large variety in molecular weight so that conservators can choose one with a matching viscosity, bonding strength, and glossiness.

In practice, Aquazol 500 has a relatively high molecular weight that might have difficulty penetrating cracks in the paint layer3, which matches this workshop’s result. However, the same molecular weight of Aquazol is also good for consolidating gouache paint because of its high bond strength. Therefore, it depends on the goal of usage of the adhesive to determine if it is a good adhesive.

Footnotes

1 Grimaldi, N., 2013. Approaches to Consolidation and Adhesives in Easel Painting Conservation. [Powerpoint] Northumbria University, Newcastle.

2 ‘for collections of furniture, ivory, metals, and oil paintings — RH fluctuations are important while most forms of incorrect temperature are not. ‘Michalski, S., 2018. Agent of Deterioration: Incorrect temperature [online] Canada.ca. Available at: [Accessed 29 January 2022].

3 Arslanoglu, J., 2004. Aquazol as used in conservation practice. Western Association for Art Conservation Newsletter, 26(1), pp.10-15.

Bibilography

Arslanoglu, J., 2004. Aquazol as used in conservation practice. Western Association for Art Conservation Newsletter, 26(1), pp.10-15.

Genty-Vincent, A., Eveno, M., Nowik, W., Bastian, G., Ravaud, E., Cabillic, I., Uziel, J., Lubin-Germain, N. and Menu, M., 2015. Blanching of paint and varnish layers in easel paintings: contribution to the understanding of the alteration. Applied Physics A, [online] 121(3), pp.779-788. Available at: <https:// www.researchgate.net/publication/282547233>.

Grimaldi, N., 2013. Approaches to Consolidation and Adhesives in Easel Painting Conservation. [Powerpoint] Northumbria University, Newcastle upon Tyne.

Michalski, S., 2018. Incorrect temperature - Canada.ca. [online] Canada.ca. Available at: <https://www.canada.ca/ en/conservation-institute/services/agents-deterioration/ temperature.html> [Accessed 29 January 2022].

Workshop 4, Northumbria University

Inpainting theoryColour matching

1 Introduction

Mixing a matching colour for inpainting can help with the Munsell colour system. In the system, colours are identified by three dimensions: value (lightness/darkness); hue (attribute of a colour in the colour wheel); and chroma (saturation/intensity).

2 Methodology

2.1 Grisaille tone gradations

• A nine-step tonal value range from neutral black to white is executed on the provided watercolour paper.

• The tone gradation was repeated with a ‘warm’ and 'cool' black, with addition of burnt sienna and ultramarine repectively.

2.2 Hue and tone mixings

• Two paint colours were applied on the top leftmost and rightmost of the 5x5 grids box.

• The secondary and two tertiary hues were mixed and put on the top line of box to form a gradation of the two paints.

• The colours were gradated their tonal value to the lightest one possible.

2.3 Chroma and value

• A saturated colour paint was chosen and altered its value by achromatically adjusted grey

3 Result and Discussion

3.1 Grisaille tone gradations

3.2 Hue and tone mixings

Check with Black and White filter on a phone or a computer

When adjusting the pigment's chroma by adding black or white, the value of the pigments also changes. Therefore, mixing an achromatic, or a ‘neutral’ grey, with matched value for the colour is essential.

The grisaille gradation is the starting point of adjusting the achromatic grey. Grisaille is a painting technique by which an image is executed entirely in shades of grey. Artists often employ the ‘warm’ and ‘cool’ tones to refer to colours tending to red/orange or blue/green, respectively. However, the terminology is imprecise. For example, French ultramarine has red under hues which can be considered as a ‘warm blue’.

Colours might have different tinting power which affected the mixing of colours. When two colours with a large difference in their tinting power are mixed, the stronger tinting colour requires less amount than the weaker one to achieve a balanced secondary hue. The amounts of both colours are even more difficult to manage when mixing a tertiary colour. By comparing the primary colours and the colour wheel, the correct tertiary colour can be made by trial and error.

Same intensity of grey for boxes on each row represents they have the same tonal value

Bibilography

Encyclopedia Britannica. 2022. grisaille | painting. [online] Available at: <https:// www.britannica.com/art/grisaille> [Accessed 8 February 2022].

Munsell Color System. 2022. Color Matching from Munsell Color Company. [online] Available at: <https://munsell.com/about-munsell-color/how-colornotation-works/> [Accessed 8 February 2022].

Workshop 5, Northumbria University

Adhesives and Facings

1 Introduction

Adhesives used in a wide range of use in conservation and the properties of different types of adhesives should be well known before treatment. In the first part of this workshop, 12 types of adhesives with various concentrations were tested on a canvas to observe their properties such as flow, saturation, and transparency.

In the second part, adhesives were applied to both a printed planar canvas sample and a rough sample for testing facing technique and properties. 4 types of facing papers were provided for evaluating the processes and to make informed choices when proceeding with treatments.

In the third part, a full facing is applied on the entire surface of a sample painting with BEVA 371 in a ‘Union Jack’ pattern.

Pic 1. Applying full facing of eltolene paper with BEVA 371 adhesive

Pic 2. The 'Union Jack' pattern for applying a full facing

2.1 Adhesives tested on a plain canvas

• Gelatine/water 1%, 5%, 10%

• Isinglass/water 1%, 5%, 10%

2 Materials and Methodology

• Plextol B500/water 50%, 70%, 100%

• Plextol K360/water 50%, 70%, 100%

• Plextol D498/water 50%, 70%, 100%

• Jade 403N /water 50%, 70%, 100%

• Aqazol 50/water 5%, 10%, 15%

• Aqazol 200/water 5%, 10%, 15%

• Aqazol 500/water 5%, 10%, 15%

• Aqazol 500/Acetone 5%, 10%, 15%

• Paraloid B72/Xylene 5%, 10%, 15%

Adhesives were prepared from its solid or aqueous form

2.2 Adhesives tested for facing

• Aqueous Adhesives

‧Isinglass 10%

‧Methyl Cellulose3%

‧Klucel G 3%

• Solvent-based Adhesives

‧BEVA 371

2.3 Tissues tested on a printed canvas sample

• Tarantula Tissue

• Eltolene Tissue

• Tengujo paper

• Kozo paper

2.4 Adhesive used on the full facing

• BEVA 371

Sample plain canvas were divided to 20 grids for testing different adhesives and facing tissue combinations listed in 2.2 and 2.3

5.

Sample rough canvas

Pic 6.

Applying facing with brush on the sample rough canvas

Pic 7.

Sample canvas for full facing using method in Pic 2.

Pic 3.

Pic 4.

Pic

3 Result

3.1 Plain canvas adhesives test reult sample, light in 45° against surface from left

3.2 Facing tested on plain sample

3.3 Facing tested on rough sample

Pic 8.

Full facing of eltolene tissue was applied onto the sample canvas with BEVA 371 in the fumehood and wait dry for a day

The facing was removed using moistened pads of white spirit

Sample canvas after facing removed will have some remaining adhesive on top

Pic 9.

Pic 10.

4 Discussion

4.1 Adhesives

The following table summarised the properties of the tested adhesives.

Table 1. Adhesives handling properties

Adhesives Viscosity ( ★ to ★★★★ : low to high)

Gloss Colour (transperant if not specified)

Transparency (only types with colour)

Other comments

Isinglass 1% ★ matt Warmed with water bath 5% ★ matt 10% ★★ matt light yellowish high

Gelatine 1% ★ matt warmed with water bath 5% ★★ matt

Plextol B500

10% ★★ satin

50% ★ low gloss white, but not observed when applied on the surface high texture of thread are filled with white adhesives and become less observable 70% ★★ medium gloss medium

100% ★★★ high gloss white low

Plextol K360 50% ★ medium gloss white high70% ★ medium gloss high100% ★★ medium to high gloss medium -

Plextol D498

50% ★★ medium gloss white medium70% ★★ medium gloss medium100% ★★★★ high gloss medium -

Jade 403N 50% ★ matt white medium reversibility decreases with time 70% ★★ medium gloss low 100% ★★★★ medium gloss low

Aquazol 50 5% ★ matt10% ★★ medium gloss15% ★★★ high gloss -

Aquazol 200 5% ★ matt10% ★★★ low gloss light yellowish high15% ★★★★ low gloss medium yellowish medium -

Aquazol 500 5% ★★ matt10% ★★★ matt15% ★★★★ low gloss -

Aquazol 500 in Acetone 5% ★ matt dries very quickly compared to aquazol in water solution 10% ★ matt 15% ★★ high gloss

Paraloid B72 in Xylene 5% ★ matt dries very quickly 10% ★★ low gloss 15% ★★★★ medium gloss

4.2 Facing tissues

Tarantula tissue

Great on plain canvas with most of the adhesives. It allows most medium-flow adhesives to penetrate well and easily take off with solvent. The tissue is strong, so it does not tear easily when applied or taken off. However, it is hard to apply on a rough surface. It stuck on the brush instead of the surface, resulting in much more adhesives required when compared to the amount used on a plain surface.

Eltolene tissue

The properties of eltolene tissue are similar to that of the tarantula tissue, but the penetrating effect for adhesives is higher in eltolene tissue. Adhesives with a low flow rate may be over-penetrated and leave too many adhesives on the surface after removing facing tissue. It is good to use a low-flow adhesive and some solvent-based adhesives, as they dry very quickly and need a tissue that can allow them to penetrate quickly.

Tengujo paper

The thinnest among the tested tissues, the strength is not as strong as the previous two. When applied with water-based adhesives, it is easier to remove the tissue by cotton swap as tengujo strength decreases when wet. When tengujo paper is applied on a rough surface, it does better than other types of tissues as it is thin and can attach well to the slight gaps on the impasto. It also requires fewer adhesives than other types of tissues.

Kozo paper

The thickest among the tested tissues and most moderate-flow adhesives cannot penetrate well. It hardly adheres to both plain and rough surfaces. Moreover, it left residues of small paper pieces on the facing after being removed. It is not a good option in most cases, but it worked well on some occasions, for instance, using Kucel G on a rough surface.

Bibilography

Alba, P., Martín-Rey, S. and Doménech-Carbó, M., 2019. Analysis of facing materials used as remoistenable temporary supports for facing on canvas paintings. CeROArt, (11). Grimaldi, N. 2019. [Powerpoint] ‘Applying Facings -Supportive Treatments’ ‘Khartasia’. 2010. Mnhn.Fr <https://khartasia-crcc.mnhn.fr/en> [accessed 24 November 2021] Murphy, Sue B., and Siegfried R. 1985. ‘A Study of the Quality of Japanese Papers Used in Conservation’, The Book and Paper Group Annual, 4 <https://cool. culturalheritage.org/coolaic/sg/bpg/annual/v04/bp04-08.html>

Workshop 6, Northumbria University

Surface dirt removal by aqueous solutions

1 Introduction

Surface dirt cleaning is the first procedure in recto cleaning.

In this workshop, various aqueous cleaning solutions were tested firstly on a sample dirtied canvas, then followed by testing on the actual project painting.

2 Materials

Aqueous solution tested

• Water

• Saliva

• Ammonium hydroxide pH 8.5, 9, 10 , 11

• Diammonium hydroxide (DAC) 1%, 2%, 3%, 4%

• Triammonium hydroxide (TAC) 1%, 2%, 3%, 4%

Pic 1 Solution tests with magnifacation light

Pic 2 Solution tested

Pic 3 Check the pH of the solution is as marked before used

3.1 Dirt-coated sample

• Small tightly rolled cotton swabs are being used

• Swab should be rolled gently over the test area until the swab becomes dirty

• Once dirty, the swab should be replaced, and the process continues until the swab no longer discolours

• The number of swabs to clean a tested area is counted

• Repeated the test with various tested solutions

• Some cleaning materials require a postapplication cleaning to clear out the active agent, such as enzymes in saliva, and chelates solutions like DAC and TAC

Pic 6

Solution test result

TAC 2% was chosen to be the cleaning agent to clean 1/4 of the painting .

Pic 4 Dirt-coated sample

3.2 Actual Painting Solution Test

• Repeat the solution test in 3.1 in the actual painting

• The best cleaning solution for the painting is chosen upon the cleaning effect, number of swabs and strength of the solutions

• The chosen solution is tested on all colour fields to establish full efficacy of cleaning

3.3 Actual Painting Dirt Removal

• A safety margin test is carried out in the margins before cleaning the middle area of the painting

• Once a satisfactory result is obtained, a larger area is chosen to clean

4 Result

Painting after cleaning 1/4 part on the top right, under:

visible light (Left);

UV fluoroscence (Right)

Pic 5 Solution test on sample

Pic 6 Solution test on the actual painting

Pic 7 & 8

5 Discussion

Ater doing the solution tests on various colour regions including the red leaves area, NH 4 OH pH9 was chosen to be the cleaning agent instead of TAC 2% in the beginning. However, when cleaning the red leaves in the top right corner, which have severe shrinkage cracks, the red pigments tend to be removed by NH4OH.

It is found that the same kind of paint can react to the same solution differently in different regions. The shrinkage cracks have hugely affected the stability of the paint layer and hence are much more sensitive than the red paint in an area without cracking.

Pic 9 Shrinkage cracks specific to the red leaves' region. Red circle indicates the region that have the cracking pattern. Note that there are the same red paints on other region (such as left edge), only the red paint in the circle is water sensitive.

NH 4 OH was chosen first instead of TAC 2% because it does not require the rinsing water layer after application, hence reducing the time of the painting to contact with moisture. Besides, TAC is a more powerful agent in this painting that cleans more patina than NH4OH, which might tend to overclean the painting.

Finally, TAC 2% was applied with an additional rule that one certain area can only be rolled with limited numbers of swabs to reduce the chance of overcleaning. In the future, other cleaning materials such as gel can be tested.

Workshop 7, Northumbria University

Humidification Treatments & Pre-stretching

V1 Introduction

arious humidification procedures were tried to correct typical planar distortions on canvas paintings.

Both pre-lining treatments and localised treatments were examined.

Fig 1 Applying moisture to some brown parcel paper strips for prestretching on a loom

2 Localised Moisture Treatment

Fig 2 The sample canvas for testing various methods and applications, front

Fig 3 The sample canvas for testing various methods and applications, back

The materials listed in the order from the bottom (nearest to the canvas) to the top. A weight is added on top of all application methods to ensure good contact with the canvas.

Each application had been tested for both 10 and 20 minutes if not otherwise specified.

1. Wet blotting paper

2. Thick Sympatex + wet blotting paper + Melinex

3. Thin Sympatex + wet blotting paper + Melinex

4. Thick Sympatex + wet blotting paper + Melinex + ironing at 40°C

5. Laponite RD 5% w/v gel (1 min) --> blotting paper (10 mins x 4 times) with ironing

6. Laponite RD 5% w/v gel (5 min) --> blotting paper (10 mins x 5 times) with ironing

Fig 5 The Laponite RD, a synthetic layered silicate gel which is insoluble in water but hydrates and swells to give clear and colorless colloidal dispersions.¹ Used in methods 5) and 6)

Method

•

2.2 Results and Discussions

To summarise, moisture and heating contributes to flattening the canvas However, some paint may become extremely sensitive when both heat and moisture are applied. A moisture and heating test should be performed before any treatments.

Fig 8 The sample canvas after all tests, having less planar distortion

Fig 7

4) Thick Sympatex + wet blotting paper + Melinex + ironing at 40°C.

Fig 6 The edge of blotting paper should be feathered by hand torn to avoid damaging the verso

Fig 4 Method 1) Wet blotting paper only.

3 Localised Humidifying Chamber

If a painting is too fragile for any heating and direct wetting method, a self-made localised humidifier can be applied on the back of the painting.

• 4.1 Materials

• Loom

• Brown parcel paper strips

• Gummed paper tape

• Sponge

• Container for water

• Scissors and ruler

Fig 9 Measured a thick Melinex and cut it into a small box. Punch a hole in the centre of the top of the box.

Fig 10 Tide a cotton ball with a fishing line and pass through the hole on the top of the box

Fig 11 Wet the cotton and place the localised humidifier on the back of the painting. Beware that the cotton ball cannot contact the canvas. A weight can be added if the condition allows. The box is placed for at least for 3 hours to allow moisture delivery.

4 Paper Stretching on a loom

Fig 12 Materials for pre-stretching a whole canvas

4.2 Methodology

Fig 13 Preparing the paper strips by cutting them into suitable lengths to attach to the whole edges of the loom. Dampened with water.

Fig 14 Place moistened paper strips on the opposite sides of the loom. They should just touch the fold edge of the painting. Attached with gummed tape by moistened it.

Fig 15 Once all the strips are placed on the edges of the painting, place the loom over the strips. Measure to make sure the loom is centered.

Fig 16 Wet the outer edges of the loom and gently fold up and stick the strips so that they wrap around the loom. The loom is then placed on an easel and let dry for at least 24 hours. During the drying process, the shrinkage of the brown parcel paper strips tensioned and straightened the canvas. This is called the drumming effect.

Fig 17 & 18 After 24 hours, carefully remove the attached paper strips and tapes by moistening them with a sponge. Never cut the canvas from the loom when under tension because this could cause the painting to rapidly spring back.

Paper stretching can potentially exert fairly strong stresses on the painting. The canvas may have to repeat the process in order to have a satisfactory result.

The edges of the canvas need to be long enough to allow space to adhere the paper strips. Therefore, not all paintings are suitable for this pre-stretching method.

Last but not least, conservators must be extremely careful not to wet the canvas centre during the whole treatment. Canvas is usually very vulnerable to water and may also shrink when moistened. The treatment includes the use with a lot of water, extra care should be taken.

5 Humidity Chamber

(Demonstration)

Bibilography

A humidity chamber contains a saturated salt solution to produce a specific level of relative humidity and is controllable .

Compared to localised moisture treatments, humidity chamber can apply moisture more evenly and more controllable. It also potentially treats surface distortions besides planar deformation such as cupping and cleavage paint.²

1 Goddard, P. (1989) “Humidity Chambers and their application to the treatment of deformations in fabric‐supported paintings,” The Conservator, 13(1), pp. 20–24. Available at: https://doi.org/10.1080/01410096.1989.9995043.

2 LAPONITE RD Data Sheet (2013) East8west.com. BYK Additives and Instruments. Available at: https://east8west.com/data/BYK_Laponite_RD_EN.pdf.

Fig 19 Sample after treatment.

Fig 20 A humidity chamber for paintings

Workshop 8, Northumbria University

Thread to thread bonding

Tools

T1 Introduction

o explore the various techniques commonly used for repairing broken thread and mending tears in canvas paintings.

By experimenting with different types of joints, tools, and adhesives, the procedure of localised structural repair is familiarised and practical dexterity is developed.

Fig 1 Thread-to-thread bonding practice with BEVA film

2 Materials

• Hooked dental instruments

• Cross blocking & normal tweezer

• Insect pins & other entomology tools

• Heating needle & spatula

Adhesive

• Solvent based adhesives

• Heat-seal adhesives

• Epoxy resin (tested only, not recommended)

Fig 2 (above) A heating needle Fig 3 (below) Various shapes of tweezers

Fig 4 The sample of broken linen thread of varying lengths for experimentation and re-joining.

3 Methodology

The materials will first try on a broken thread sample, then on an actual painting sample.

Fig 5 Apply adhesive to the end of broken thread. Trim, groom and manipulate the threads into various joints. Repeat the test with other adhesives. Hold the bonding with a tweezer until set.

Various joints have been tested:

• Butt Joint

• Lap Joint

• Scarf Joint

• Bridging

• Twisting

Fig 6 For heal-seal adhesive, a heated spatula or needle is required.

Try the technique on the real painting sample, with the use of ‘sight master’ to magnify the view.

Fig 7 The real painting was laid down on a table with thin board support in the treating area, between the canvas and the stretcher bar.

4 Result & Discussion

Among all types of joints, the butt joint is the easiest to perform as it does not require further manipulation of the thread before joining. However, the butt joint is weak when compared to most of the other types of joints, because the contact surface area for the two ends of the thread is the smallest and thus the sheer strength is small.

A lap joint or a scarf joint is possible when the two ends of the thread are in excess length. They require shaping the ends of the threads with a scalpel. This action can easily make the ends disrupted. Applying deionised water by brush to groom the ends can help reshape its shape if necessary.These joints are stronger in terms of tensile and sheer strength but harder to handle.

Conversely, when the thread is too short, a bridge joint is required. Bridging is performed by adding an extra strip of thread between two ends of the thread, resulting in a bulking appearance. For the choice of additional thread, ideally, using extra threads from the edge of the same canvas can give a similar strength to the original thread. However, sometimes it may not be possible, and a new thread is added. The strength of the new thread is higher than the original, which causes unusual tension to build up on the bonding.

Fig 8 Results of the broken thread sample. The threads are aligned as stright as possible for the best result in the actual practice.

Fig 9 The tear before treatment, actual painting sample

Fig 10 The tear after treatment. As time is limited in the workshop, only a small area has been done. The threads are extremely fragile and therefore butt joint and bridging were chosen.