HISTORICAL BOLE WORKSHOP
Guildhall Art Gallery - 18th to 20th June 2018
Course Tutor: Rhian Kanduth (Oil & Water gilding Specialist and Tutor at City & Guilds Art School)
After running a successful Historical Bole Workshop in June, we decided to provide a thorough description of the contents covered in the workshop. We hope you find this information useful and even helpful to your professional practice! You can find a version of this same document with pictures in the 'News & Events' section of our group.
This three day workshop focused on the techniques used in production, application and finish of Historical Bole colours used in the preparation of gilded surfaces. The course provided the opportunity to make a test panel with an array of colours, both traditional and bespoke from a variety of bole suppliers. It was also a chance to learn about colours used during particular periods in decorative art history and the countries that favoured them.
Bole is coloured pipe clay that is applied to a gesso substrate before gold leaf is applied. The platelet structure of the clay used, combined with a cushioning gesso layer enables gold leaf to be burnished to a high shine. One of the key aims of this course was to experiment using different bole colours under different shades and thicknesses of gold leaf and how the finish can differ when burnished or distressed. It is key to understand the subtleties of gold leaf, the underlying bole colour as well as the finishing method applied, particularly if these are to be used to create invisible repairs to decorative surfaces using these techniques.
PREPARATION OF THE BOLE
The course began by preparing a dry bole from a London based stockist, AS Handovers. These dry boles require grating and soaking in a small quantity of distilled or deionised water, preferably overnight, to soften them. At this stage, the soft clay (a walnut sized amount) can then be mullered to ensure the pigment particles are as fine as possible.
Once mullered, the resulting paste can be blended with blood warm rabbit skin size 1:12 (rabbit skin glue granules: water) to make a solution that is approximately the consistency of milk. Once the mixture is well blended this should then be strained at least once to remove any remaining lumps or larger particles – fine nylon stockings are perfect for this. A ‘glass test’ can also be used at this point - lift the brush loaded with the mixture up the side of the beaker or jar – if the bole is suitable for use it should not be too translucent and there should be very few pigment particles remaining – if there are, try straining again.
Once the warm rabbit skin size has been added to the pigment/clay paste, only a minimal amount of heat should be applied in order to keep the bole liquid. Sitting the jar of prepared bole in warm water is enough to prevent the size from gelling. The bole should not be allowed to overheat as the protein molecules can lose their original properties, preventing the bole from functioning as it should. This could cause the finished gilding to deteriorate over time.
COLOURS AND APPLICATION OF THE BOLE
To apply the bole, use a soft sable brush or ‘mop’ in sweeping brush strokes. Avoid a quick succession of repeated strokes as the size within the bole dries quickly and can create drag marks. The first couple of coats are likely to look unsatisfactory, however, as the coats build up, so do the layers of pigment and size creating a smooth opaque finish.
Black bole shades often require more layers of application as the pigment particles are not as opaque. Avoid using Lamp black pigment when making bespoke bole colours as its production method introduces oil and therefore the bole can become greasy and unusable. 4-6 coats of bole should be ample depending on the colour being used, but this also depends on the desired effect.
Yellow and red are the most commonly used clay bole colours and have been used by the Ancient Egyptians, the Romans, and Victorians and are still commonly used today. Red provides a distinct effect when the gold leaf is distressed and shades of yellow are commonly used as an initial base primarily as the similarity in colour to gold assists with the gilding process because skips or losses are more difficult to see which makes gilding complex shapes and ornament much easier.
Several traditional shades of red and yellow were made during the workshop, followed by a range of bespoke colours which were created by using carefully measured blends of the traditional shades. For example - ‘Georgian Orange’ - a combination of Sinopia Yellow and Spanish Red.
BOLE COLOURS TESTED:
1. Sinopia Yellow. Wet (Sinopia San Francisco)
2. Sinopia Yellow Wet + Spanish Red (Gilding Supplies) = ‘Georgian Orange’ 50:50 Ratio
3. Spanish Red. Wet (Gilding Supplies)
4. Wet Red (S. Stevensons)
5. Wet Red (S. Stevensons) + Dark Blue Dry (Handovers) = ‘Victorian Plum’ 2:1 Ratio
6. Dark Blue. Dry (Handovers)
7. Black Dry (Handovers) 1-2% + Light Blue Dry (Handovers) 2-4%+ White Dry (Handovers) 95% = ‘Cold Grey’.
8. Baroque Brown Wet (S. Stevensons) 6 - 8% + White Dry (Handovers) 90+% = ‘Warm Grey’
9. Sinopia Black. Wet (Sinopia San Francisco)
10. Green. Dry (Handovers) 5% + White. Dry 95% (Handovers) = ‘Adams Green’
11. Light Blue (Handovers) Dry = ‘Adams Blue’
12. French Red (S. Stevensons) 3 % + Baroque Brown. Wet 1% (S. Stevensons) + White. Dry 95% (Handovers) = ‘Georgian Pink’
The two bespoke shades of grey would most likely have been seen in the English Regency Period and the pastel colours that were made (particularly the Adam’s Green/Blue and Pink) would commonly be used during the Georgian Period. Darker colours, such as Plum and Black are seen regularly beneath the burnished and distressed water gilding of the Victorian Period.
It is common to see yellow bole with red highlights on high points of decoration, and this was done as the suggestion was that red bole could be burnished to a particularly high shine due to the nature of the particular clay particles, which is true to an extent, however, yellow bole can also be burnished to a high shine as long as the pigment particles are suitably ground. The Sinopia Yellow trialled here perfectly highlighted this as it produced a beautiful base for gilding and actually burnished better than most of the other colours sampled. Often, where red bole is used, it can be lightly distressed allowing the red to show through, so the effect that this creates is perhaps as much about the colour used as the high shine that could be achieved.
AFTER THE BOLE DRYING
Once the layers of bole are dry, the surface of the bole must be prepared. Although bole is relatively smooth at this stage it is advised that the rough edges are taken down. There are several ways of achieving a suitable finish. Lightly rubbing the surface with fine grade sandpaper or using bristle brushes that have been cut flat have a similar effect. Avoid using wire wool to polish bole, particularly on lighter colours as it can be greasy and this can affect the application of the gold leaf. It is always advised to avoid touching the bole layer as much as possible to avoid adding oil from your hands for the same reason.
Once the bole layer is ready for gilding the gold leaf can be applied. I tested three gilding water solutions at the workshop:
London Dry Gin or similar inexpensive supermarket own brand gin (this has a higher water content!)
225 ml of water with ¼ tsp of 1:12 Rabbit skin size + 1 tsp of IMS (WEAK)
225 ml of water with ½ tsp of :12 Rabbit skin size + 1 tsp of IMS (STRONG)
The gin worked the most effectively – the gold adhered evenly and dried to a very smooth finish without having to tamp down any lifting areas.
Adding a small amount of rabbit skin size can help if the gesso/bole layers have been left a little while before gilding. We were gilding 24 hours following bole application which is an ideal amount of time to leave between these two stages. Adding size to gilding water can also stain the gilding upon drying, and this is particularly difficult to avoid if faulting small areas of missed gilding so should be avoided if possible.
For my test panel I trialled two types of gold leaf over each bole sample. Firstly, Wrights of Lymm 23.5 Ct Finest Quality Gold and secondly Handovers 23ct Extra Thick Gold. Extra thick is approximately three times thicker than standard leaf. This is particularly useful if gilding a slightly rough or complex surface, for example punch work or sanding, as it moulds around the surface textures more readily. The two colours sampled were almost identical in tone however handling this type of leaf is quite different – something I had not noticed before. The thicker gold is ‘heavier’ and so is much quicker to attract to the size water and it distresses fractionally slower.
Applying a sweep of gin with a soft brush to the prepared bole surface the leaf was applied and left to dry for at least an hour before faulting any missed areas or where the gold had not taken.
At this stage, lightly tapping the surface of the bole enables the gilder to tell if the surface can be burnished. The sound should not be too dull, as this will mean there is still moisture there. A light tapping sound should suggest that the surface is ready for burnishing – the longer you leave it from this point the less burnish you will achieve. A useful tip here is to run the agate burnisher over the surface only lightly initially in one direction only, increasing the pressure until the desired burnish is achieved. ‘The gold then becomes almost dark from its own brilliance’. 1
Overall, the two types of gilding trialled here both burnished really well on all of the bole colours sampled, however, the finer burnish was achieved on the 23.5 Ct gold samples. In relation to specific bole colours, by far the greater burnish occurred on the two Sinopia colours, yellow and black. An extremely fine, high shine finish was achieved here.
DISTRESSING THE GILDING
Distressing the gilding was an important stage of the workshop. This is where the surface of the gold can be lightly worn back to reveal the underlying bole colour. Here we used very small amounts of dry pumice powder and small cotton wool swabs lightly brushed over the surface in a circular motion.
Alternative distressing techniques are entirely dependent on the desired effect. Another dry method would be to use Micromesh fine abrasive sheets which are available in several different grades. Wet methods can also be used – such as swabs with saliva or very weak rabbit skin size – these methods are slightly more difficult to control however so should be approached with caution.
This workshop was so enlightening. It provided an opportunity to make and test a variety of bole colours that I would rarely get to use, and compare and contrast their performance. It was also an opportunity to meet with like-minded individuals working in the field (predominantly Frame and Furniture Conservators) to discuss alternative techniques and methods for surface preparation, gilding, burnishing and distressing. I am looking forward to using my knowledge on future projects at the NPG – in particular the Jonathon Swift (NPG 6191) Frame Conservation project where I will be replacing a large percentage of the yellow bole, as much of the original has been lost before a later gilding scheme has been applied. This project has been generously funded by the Elizabeth Cayzer Charitable Trust and there will be more updates on the progress of this project over the coming months.
A.S Handover Ltd. - For Brushes Paints, Gold leaf & Sundries
1 Farleigh Place,
London N16 7SX
Stuart R. Stevenson - Artists & Gilding Materials
Stuart R. Stevenson
68 Clerkenwell Road
L. Cornelissen – Artists’ Colourmen
105 Great Russell Street,
Wrights of Lymm – Gold Leaf Specialists Wright House
Cennini, C., & Thompson, D. V. (1960). The craftsman's handbook: The Italian "Il libro dell' arte." Translated by Daniel V. Thompson. New York: Dover Publications.
Mactaggart, P & A (1984) Practical Gilding. England. Mac & Me Ltd.
Rivers S & N Umney (2003) Conservation of Furniture (Ch.14) Oxford. Butterworth – Heinemann