Porcelain

What is Porcelain?

Soft-Paste Porcelain was first developed in Europe in1738 to imitate Chinese porcelain. It was produced by mixing white clay with a frit (a glassy substance that was a mixture of white sand, gypsum, soda, salt, alum and nitre). Lime and chalk were used to fuse the white clay and the frit; the mixture was then fired at a lower temperature than hard-paste porcelain. It produced a softer body than hard-paste or true porcelain being fired at 1200°C. Soft-paste porcelain is soft and the body is granular since the ingredients do not melt together.

Hard-Paste Porcelain is a white, vitrified, high-temperature ware, which is translucent and rings when struck. A unique aspect of porcelain is that it can be worked as clay, but when fired properly reaches a state similar to glass. In China, the term ‘porcelain’ is more widely applied to include non-translucent fine stonewares. It is a special type of clay either white or grey, to which kaolin (a white firing stiff clay) and white China stone (finely decayed granite, washed and prepared as small white blocks) is added. When fired at temperatures of 1,280°C and over (up to 1,400°C was achieved by the Chinese), the body vitrifies, i.e. it becomes completely impermeable. Glazes can be applied for the first firing, or a vessel can be decorated with a low-firing glaze and put back into the kiln a second time. True porcelain was being made in China and Korea around 960 AD. Hard-paste was firstly made in Europe in the C18th, its recipe being discovered by Meissen chemists in Germany.

Porcelain

 

Case Study: C17th Blue and White Chinese Porcelain Bowl

Hard-paste, thrown, porcelain bowl with under glaze cobalt blue floral/organic decoration to both the interior and exterior. 4 labels were applied directly onto the base 2 detailed that the bowl was retrieved from a sunken vessel off the island of St. Helena in 1613. The object was broken into 5 fragments and one large section was missing.

Avoiding previously restored areas, surface dirt was loosened with a weak solution of non-ionic detergent in deionised water, applied by stencil brush. Then, the surface was swab cleaned with deionised water only. The whole surface was further swab cleaned with acetone
All edges were degreased with acetone, applied using a stencil brush. The fragments were bonded using a water-white epoxy resin and were aligned and held in position with various combinations of clamps and supports.
A barrier layer of a 10% solution of acrylic resin in acetone was painted along all break edges. Then, a core fill was modelled in-situ with Fine Surface Casting Plaster. When cured, this was cut back so that it sat just less than 1mm from the surface of the glaze. This core fill was then consolidated with a 10% solution of acrylic resin in acetone.

It was agreed with the client that the missing decoration on the exterior would not be replicated; to give clear distinction between original and non-original materials. However, the interior surface of the fill was finished to be a close match to the original. The glaze layer to the interior was mimicked using a coloured epoxy paste; a mix of water-white epoxy resin, fumed silica and Artist’s Dry Powder Pigments. The colour of this fill was taken to just a tone away from the colour of the ‘true’ glaze. Once cured, the decoration on the interior was replicated as follows:
Areas corresponding to the missing blue decoration were cut back from the colour-fill and then these areas were inlaid with a blue epoxy fill. Lines were also scored into the main large fill and in-filled to mimic the cracks/crazing within the glaze Once cured, after 48 hours, the colour fills were refined and polished with various grades of sanding fabric.

 Finally, the colour of the exterior in-fill was further toned with a mixture of a Water-Borne Ceramic Glaze, Artist’s acrylic paints and Artist’s Dry Powder Pigments. The final layer was polished with various grades of sanding fabric and then with Plastic Polish.

(images reproduced with permission of Birmingham Museums & Art Gallery)

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Case Study: Chinese hard-paste porcelain saucer. Qing dynasty, Qianlong period (1736 - 1795), ca 1745

Surface dirt was loosened with a weak solution of non-ionic detergent in deionised water, applied by stencil brush. Then, the surface was swab cleaned with deionised water only. All edges were degreased with acetone, applied using a stencil brush. The fragments were then bonded using a water-white epoxy resin and were aligned and held in position with various combinations of clamps, tape and supports.
The large missing area and chips were reconstructed with a coloured epoxy paste; a mix of water-white epoxy resin, fumed silica, French Chalk and Artist’s Dry Powder Pigments. The colour of these fills was taken to just a tone away from the colour of the ‘true’ glaze.
Research identified the missing decoration:
Once cured, after 48 hours, the colour fills were refined and polished with various grades of sanding fabric.  The reference text illustrated a similar saucer 1:1 and this was used as a guide for the in-painting of the missing design. Missing decoration was hand-painted using of a Water-Borne Ceramic Glaze, artist’s acrylic paints and Artist’s Dry Powder Pigments .This combination of retouching media was also used to further tone the exterior in-fills. This was polished with various grades of sanding fabric and with a Plastic Polish. The missing gilded decoration to the in-filled chips and large area of missing decoration was replicated using a Water-Borne Ceramic Glaze and Bronze Powders.

(Images reproduced with permission of Birmingham Museums & Art Gallery)

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Case Study: Porcelain Figurine: C19th Volkstedt Figurine Literature

All surfaces were cleaned with a weak solution of a non-ionic detergent in deionised water, followed by swabbing with acetone. Broken sections were then bonded with a water-white epoxy resin. Missing areas, such as the majority of the scroll and the book , and smaller chips were re-modelled and filled with a coloured epoxy paste; a mix of water-white epoxy resin, fumed silica, French Chalk and Artist’s Dry Powder Pigments. Once cured, after 48 hours, the colour fills were refined and polished with various grades of sanding fabric. Missing decoration was also further hand-painted using of a Water-Borne Ceramic Glaze, artist’s acrylic paints and Artist’s Dry Powder Pigments. This was polished with various grades of sanding fabric and with a Plastic Polish. The missing gilded decoration was replicated using a Water-Borne Ceramic Glaze and Bronze Powders.

(images reproduced courtesy of S. Orrett)

 

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Case Study: 1913 Royal Crown Derby Peacock

Cleaning: The peacock was swab cleaned with a weak solution of non-ionic detergent and deionised water. It was also further cleaned with a solvent.

Re-modelling of Comb: The comb was remodelled wth a putty comprised of a water-white epoxy resin and various fillers. Once cured, it was refined with files and sanding fabic.

Gilding: The comb was water gilded with 23.5ct gold leaf.

 

(Private Collection)

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Case Study: A Meissen Figurative Group

Cleaning: Surface dirt was loosened with a weak solution of a non-ionic detergent in deionised water, applied using a stencil brush. The object was then cleaned with the controlled use a Derotor Steam Cleaner GV.

Remodelling Missing Areas: The missing area of the lute was handmodelled using an epoxy paste, comprised of a water-white epoxy resin, fumed silica and artists dry powder pigments. Once cured, it was refined with sandpapers and sanding fabric and was then retouched with an arylic glaze and artists dry powder pigments.

 

(Private Collection)

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Case Study: Meissen Basket

The basket required cleaning and the remodelling of a new handle.

Cleaning: The basket was swab cleaned with a weak solution of a non-ionic detergent and deionised water, followed by controlled use of a Derotor Steam Cleaner GV.

Remodelling Missing Handle: A silicone rubber mould was taken from the existing handle. Plaster of Paris was then cast into the mould. The cast was then carved and modelled to fit onto the broken junctions of the missing handle. A silicone mould was then made of this plaster cast and then the mould used to reproduce an epoxy cast; a paste of epoxy resin, fumed silica and artist's dry powder pigments. The epoxy cast was adhered in position with an expoxy adhesive and, once cured, more epoxy paste was applied to the joins and refined. The new handle was further retouched with an acrylic glaze and artist's dry powder pigments.

 

Private Collection

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Case Study: Chinese Porcelain Bottle & Cover Kangxi period (1662 - 1772) in style

All fragments were cleaned with a non-ionic detergent and then the controlled use of a Derotor Steam Cleaner GV. A water-white epoxy resin was then used to join the fragments. Missing areas were filled with an epoxy colour fill; epoxy resin, plus fumes silica and artist’s dry powder pigments. Colour fills were refined with sanding fabric and finished with a plastic polish.

(Images reproduced courtesy of Mr. T. Massey-Lynch)

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Case Study: Jane Harrison Bisque Doll, Merchant Taylors Girl School Mascot, made by Heubach Koppelsdorf Bisque Doll, c1914

The head was broken into 7 main sections. The dry run revealed 12 obtrusive chips; 1 behind each ear, 2 to the nape of the neck, 3 around the right eye, and 2 to the forehead and 3 around the top of the head.
The doll had been previously repaired. Many of the previously repaired joins remained in tact and stable. Previously retouched areas remained unobtrusive.

Excess adhesive, from the previous repair, was present to the interior and the exterior surfaces of the head. This was removed mechanically with a scalpel. All broken edges were then cleaned with acetone, applied using a stencil brush. This also de-greased the broken edges in preparation for bonding. The fragments were bonded using water-white epoxy resin and were aligned and held in position with various combinations of clamps and supports. All chips were in-filled with a coloured epoxy paste made up of epoxy resin, fumed silica and Artist’s Dry Powder Pigments. Once cured, after 48 hours, the fills were refined and polished with various grades of cushioned abrasive cloth.
In-filled areas were further retouched by hand using a mixture of Acrylic Water-Borne Ceramic Glaze, Artist’s acrylic paints and Artist’s Dry Powder Pigments. The final layer was polished with various grades of cushioned abrasive cloth. No additional retouching was carried out to the previously repaired areas.
The plaster supports of the eyes, which had become detached when the head was broken, were consolidated with a 10% solution of acrylic adhesive in acetone. Then, the eyes were placed in position and fixed in place with the plaster supports that were adhered with a 1:1 solution of the acrylic adhesive in acetone.
The cardboard pate was repositioned, to form the crown of the head, and secured through the holes to either side of the head using fine nylon thread. The wig was then placed over the head, lining up the plait to the middle of the neck. Then, the wig was tacked in place around its edge with several small dabs of 1:1 acrylic adhesive in acetone.

(images reproduced courtesy of Merchant Taylors Girls School, Crosby, Liverpool) 

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