Earthenware

What is Earthenware?

Earthenware is a ceramic made from potash, sand, feldspar and clay. It is one of the oldest materials used in pottery. Generally, most earthenware is red in colour. However, this is not always the case, and for the modern potter, white and buff coloured earthenware clays are commercially available. Earthenware is typically biscuit fired (first kiln firing) at a temperature of around 1000 degrees Celsius (1800 degrees Fahrenheit), and glaze fired (the final/second firing) at around 1100°C (2000°F).  Sometimes it may be as thin as bone china and other porcelains, though it is not translucent and is more easily chipped. Earthenware is also less strong, less tough, and more porous than stoneware - but its low cost and easier working compensate for these deficiencies. Due to its higher porosity, earthenware must usually be glazed in order to be watertight.

Earthenware

Case Study: Mid- C17th Dutch Delftware Tile with 'Three-Dot' Corner Motif

The tile has been previously repaired; the repairs were deteriorating, misaligned and unsightly. The old repairs were dismantled using various combinations of mechanical and solvent applications. The fragments were cleaned mechanically and with controlled use of a Derotor Steam Cleaner GV.
Broken edges were consolidated with a 10% solution of a conservation grade acrylic resin in acetone and then bonded with a 1:1 combination of the same resin. Chips and missing areas were filled with either Polyfilla and/or plaster of Paris. Filled areas were retouched with a water-borne ceramic glaze and artist’s dry powder pigments (upper surface) and artist’s acrylic paints (back face). Retouched areas to the upper face were polished with polishing fabric and then a plastic polish.

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Case Study: Tin-glazed Earthenware. C19th (?) copy of one of the Putto in Swaddling Clothes by Andrea della Robbia

For the Portico of the Spedale degli Innocenti, Florence.

Upper/Glazed Surfaces:
Loose surface dirt was removed using a soft sable brush & a vacuum. Ingrained dirt was further removed using a glass fibre brush and a vacuum The surface was then cleaned by swabbing with a weak solution of non-ionic detergent in deionised water, which was then removed with swabs of deionised water only. Stubborn dirt was removed by swabbing with acetone.

Backs of the Plaque/Unglazed Surface:
Bitumen covered substantial areas of the rim. The majority of this was removed by firstly softening it with white spirit, which was applied on cotton wool pads. Once softened, the Bitumen was carved back with a scalpel blade to a uniform level.
Loose surface dirt was removed using a soft sable brush & a vacuum. Ingrained dirt was further removed using a glass fibre brush and a vacuum Finally, the exposed clay body was cleaned with conservation putty.

A 10% solution of an acrylic resin in acetone was used to consolidate loose sounding’ areas of glaze and exposed areas of clay body to the upper surfaces. This was applied by brush and also micropipette.

A 1:1 solution of acrylic resin in acetone was used to bond detached areas of glaze. The missing areas of glaze were mimicked using a coloured epoxy paste; a mix of a water-white conservation grade epoxy resin, fumed silica and Artist’s Dry Powder Pigments. A large missing area to the wall of one of the plaques was reconstructed with a core-fill of plaster of Paris tinted with Artists Dry Powder pigments to mimic the clay body. Then, a coloured epoxy paste (as above) was applied on top to mimic the glaze. Once cured, after 48 hours, the epoxy colour fills were refined and polished with various grades of sanding fabric.  Finally, these were further toned with a mixture of Water-Borne Ceramic Glaze, artist’s acrylic paints and artist’s dry powder pigments. This retouching medium was applied using an airbrush, and the final layer was polished with various grades of sanding fabric and then a Plastic Polish. Artist’s acrylic paints were used on the back of the fill to mimic the unglazed clay body.

(images produced courtesy of Mr. D. Goeritz)

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Case Study: The Conservation of a Della Robbia Madonna & Child,St Joseph's Church, Our Lady Star of the Sea Parish, Weymouth.

Condition: The tin-glazed earthenware plaque of the Madonna and Child is sited below the bell tower over the front entrance of St. Joseph's church; the church is in close proximity to Weymouth harbour. The combinations of a porous ceramic body, an ill-fitting tin-glaze and exposure to a salty environment had resulted in a large proportion of glaze loss. At some time previously, attempts had been made to disguise this damage; areas of loss had been painted over. The surface of the plaque was extremely dirty.

Treatment:A 'tapping' assessment was undertaken to identify unstable areas of ceramic and glaze. Areas of over-paint were removed mechanically using a scalpel blade. The surface was then cleaned; initially with Smoke Sponge and then a variety of solvents. Stubborn dirt and remaining over-paint was removed with the application of Enviromose; this was applied with a paint brush and left for approximately 10 minutes after which is was removed mechanically. Ingrained dirt was further removed using a glass fibre brush and also by the application of Solvol Autosol. Exposed areas of clay body were finally cleaned and degreased using acetone. Exposed areas of clay body and lifting areas of glaze were consolidated with an acrylic dispersion.The missing areas of glaze were mimicked/in-filled using a coloured polyester resin paste. Once cured, after 1 hour, the polyester colour fills were refined and polished with various grades of Micro- Mesh and files. These were further toned with a mixture of Rustins Acrylic Water-Borne Ceramic Glaze, and Artist's Dry Powder Pigments. This retouching medium was applied by brush, and the final layer was polished with various grades of Micro- Mesh and then with Greygate Plastic Polish. A protective layer of Araldite 20/20 was applied over in-filled and retouched areas.The painted mortar that surrounded the plaque was retouched to achieve a more accurate colour for the ceramic. This was done using Rustins Acrylic Water-Borne Ceramic Glaze, and Artist's Dry Powder Pigments.

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Case Study: 1722 Liverpool Delftware Plaque from Merchant Taylors Boys' School, Crosby, Liverpool

A dated Liverpool delftware plaque; biscuit coloured fabric with tin-glaze and cobalt blue decoration. Decorated with the armorial of Merchant Taylors and motto, and inscribed, “THIS SEAT WAS ERECTED BY JOHN HARRISON AND HENRY HARRISON OF LEVERPOOLE 1722”. This plaque commemorates the purchase of a pew in 1722 by John and Henry Harrison, who were related to the school's original founder, John Harrison. It was sited in St. Michael’s Church in Crosby, Liverpool, on the wall over the pew near the middle of the church. It is thought to have hung in the church until it was demolished in the C19th, after which it was acquired by the school. It was made at the pottery of Alderman Thomas Shaw, which was at the end of Fontenoy Street and Dale Street in Liverpool

On receipt of the plaque, previous repair was present; it had been broken into three sections, repaired with an epoxy resin, missing areas in-filled with epoxy resin and titanium dioxide, and retouched. The alignment of the sections was very good and the joins appeared strong and stable. Retouched and in-filled areas had discoloured and, overall, much dirt was ingrained on the upper and reverse surfaces. Numerous chips and wear were present along all four edges and corners; a characteristic of this type of pottery; as low-fired and with a thick glaze, it is prone to chipping and glaze loss. As the glaze had been applied thickly, it had crawled in several areas, almost peeling and pulling back from the clay body, creating deep pits and exposing substantial areas of clay body, particularly to the right hand side of the plaque.

All over-painting was initially removed using a scalpel blade under magnification. The surface (both back and front) was then cleaned by firstly applying a weak solution of Synperonic A7 and deionised water, applied by stencil brush, followed by the controlled use of a Derotor Steam Cleaner GV.

As much in-fill material as possible was removed with a scalpel blade. The join lines were then painted with deionised water to form a barrier layer, followed by the application of Nitromors, after which the plaque was covered in Clingfilm to concentrate the action of the Nitromors. Prior to this various solvents had been tested to determine which one may reverse the previous repairs. Over two weeks the Nitromors was removed and reapplied, but there was no movement in the joins; it was ineffective. The plaque was finally fumed with dichloromethane in a sealed container for several days; this was ineffective.
It was decided not to continue trying to dismantle the previous joins as this could actually put the object at risk of further damage; the adhesive used in the previous repair was stronger than the ceramic body itself.

All chips, along join lines, edges of glaze and clay body were consolidated with a 20% solution of Paraloid B72 in acetone, applied by brush. The glaze layer was then mimicked using a coloured epoxy paste; a mix of Hxtal NYL-1, Cab-O-Sil ® and Artist’s Dry Powder Pigments.

Once cured, the epoxy fills were refined with various grades of Micro- Mesh™. They were further hand-retouched with Rustin’s Acrylic Water-Borne Ceramic Glaze and Artist’s Dry Powder Pigments. Retouched areas were refined and polished with Micro- Mesh™ . The chipped areas to the unglazed back face of the plaque were filled with a mixture of Polyfilla and Artist’s Dry Powder Pigments. These fills were refined with a scalpel and various sands papers and then retouched with Artist’s acrylic paints.

(Images reproduced courtesy of Merchant Taylors Boys' School, Crosby, Liverpool)


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Case Study: Quest for Treasures Touring Exhibition

The Conservation of 29 Pottery Vessels from the Collections of the National Museums Liverpool for the Quest for Treasures Touring Exhibition

This is a commercial loan produced for the Asian market by Danish company United Exhibits Group (UEG). The exhibition features the collections of major museums including PennStateUniversity, National Museums, Liverpool, Warrington Museum and Bolton Library & Museum Service.Focussed on West Africa, South America and the Middle East, the exhibition explores ideas of 19th century travel, exploration, collecting and colonialism.

The exhibition tour includes the following venues:

Chiang Kai-Sheik Memorial Hall,Taipei, Taiwan. 15th January 2013 - 14th April 2013

National Science and TechnologyMuseumKaohsiung, Taiwan. 4th May - 1st of September 2013   

Conservation

29 pottery vessels from the South American and African collections of the National Museums Liverpool were conserved in preparation for loan. All items were surfaced cleaned by firstly using a soft brush in combination with vacuum and then with Smoke Sponge. All fugitive surfaces, travelling cracks and exposed areas of clay body were consolidated with a 7-10% solution of Paraloid B72 in acetone, applied using a brush or glass micropipette. Several vessels required more extensive treatment, which involved the in-filling of missing areas for structural support with either plaster of Paris or Polyfilla. These filled areas, once refined, were retouched to the agreed level with the relevant curators.

Photographic condition reports were produced that accompanied the items on loan.

 

Case Study: Large Glazed Earthenware Garden Urn & Pedestal

On acceptance, the urn had been damaged previously and repaired with a blue silicone adhesive.

Dismantling Previous Repair: Excess silicone adhesive was mechanically removed with a scalpel blade. Various solvents were tested on the adhesive to find out if any were suitable to reverse the previous repair. The final solution was to use combinations of localised heat and blades. Cleaning: Remaining adhesive residues were mechanically removed from the break edges and this was followed by cleaning with the controlled use of a Derotor Steam Cleaner GV. Dowelling: Dowels made from carbon rod were inserted along two break edges on the wall of the vessel to provide addition structural support.Consolidation: All chips and break edges were consolidated with a 10% solution of an acrylic resin in acetone.Bonding: The fragments were bonded with a polyester resin.Reconstruction of Missing Areas & Filling Chips: Several large areas of the rim were missing. These and smaller chips, to both the urn and the pedestal,  were filled with a coloured paste made up of a polyester resin, marble dust and artist's dry powder pigments. Finishing: Reconstructed areas were refined with files and sanding fabric. The interior was retouched with acrylic paints and the exterior was retouched with an acrylic glaze and artist's dry powder pigments.Fixing Urn to Pedestal: A stainless steel metal dowel, which had a hole drilled to its centre (to provided drainage), bridged to urn and the pedestal and this was secured with a polyester resin.

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Case Study: c16th Iznik Ewer

The ewer had been repaired previously. The repair was very crude and had deteriorated with one main section missing to the rim and a substantial area to the foot. There were several additional chips to the rim.
Excessive adhesive and other residues were removed mechanically. The object was then further cleaned mechanically and with the controlled use of a Derotor Steam Cleaner GV. Staining to a travelling crack was removed using a poultice of an enzyme washing powder and deionised water. The missing areas were reconstructed by first forming a core fill of plaster of Paris. The core fills and the exposed edges of the clay body were then consolidated with a 10% solution on an acrylic resin in acetone. The missing areas of glaze were then mimicked using an epoxy paste; water white epoxy resin, plus fumed silica and artist’s dry powder pigments. Once cured the fills were refined with glass paper and sanding fabric and then finished/polished with a plastic polish. Missing decoration was replicated by various combinations of inlaying an epoxy coloured paste or hand retouching with quick drying water borne ceramic glaze and artist’s dry powder pigments. Reconstructed non-glazed areas were retouched with artist’s acrylic paints.

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Case Study: Late C19th Joseph Holdcroft Majolica Chinaman Sugar Bowl

The sugar bowl lid had been previously repaired. The repairs were very crude and were misaligned. The old repairs were dismantled using various combinations of mechanical and solvent applications. The fragments were cleaned mechanically and with controlled use of a Derotor Steam Cleaner GV. Broken edges were further cleaned with various poultices.
Broken edges and chips were consolidated with a 10% solution of a conservation grade acrylic resin in acetone and then bonded with a 1:1 combination of the same resin. Chips and missing areas were filled with either Polyfilla and/or plaster of Paris. A large missing area of the flange was reconstructed using plaster of Paris to form a core fill and the missing glaze was mimicked using a coloured epoxy paste. Filled areas were further finished by retouching with a water-borne ceramic glaze and artist’s dry powder pigments .Retouched areas were polished with polishing fabric and then a plastic polish.

(images reproduced courtesy of A.Lord)

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Case Study: Late C19th Earthenware Jug with Enamel Decoraton

The jug had been previously repaired; some repairs had failed; others were deteriorating, misaligned and unsightly. The old repairs were dismantled using various combinations of mechanical and solvent applications. The fragments were cleaned mechanically and with controlled use of a Derotor Steam Cleaner GV. Broken edges were further cleaned with various poultices.
Broken edges were consolidated with a 10% solution of a conservation grade acrylic resin in acetone and then bonded with a 1:1 combination of the same resin. Chips and missing areas were filled with either Polyfilla and/or plaster of Paris. Filled areas were retouched with a water-borne ceramic glaze and artist’s dry powder pigments Retouched areas were polished with polishing fabric and then a plastic polish.

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