Buff green Pt 1 - 12th night entry

12th Night Lochac A&S competition Entry

My entry for the Kingdom of Lochac 12th night Arts and Sciences competition in the category of "A container" is a cup based on an extant example from 12^th century Iran (Persia). This cup has been hand thrown and hand glazed by myself over the last two months. It is currently unfinished, sitting at stage 6 of 7. This accompanying documentation will discuss the extant item, the creation of the object and my development in the following sections:

• The extant object - what I've learned about how it was originally made & glazed.
• construction - stonepaste
• construction - shape
• glaze - slip
• glaze - underglaze
• reference cup summary
• Constructing the replica - stages and learning
• Glazing the replica - stages and learning
• Reflection
• References (alphabetical)
• Table - additional extant items referenced - shape

This project has taught me a lot about ceramics cups, having grown from previously only throwing one moderately successful cup under complete guidance prior to November 2019 to being able to independently form and shape the objects quite close to what I am after. I am rather pleased with the results and plan on exploring period shapes and glazes more going forward. I believe I have achieved the targeted outcome of this project and there is very little I’d change for future implementation.

The Extant Object: a beautiful cup from Iran.

Image 1. Reference cup - Cup with Floral Decoration, second half 12th–13th century, Rayy (?) Iran, stonepaste; underglaze slip-painted. 14cm tall.  (The Met Museum, Item number 1970.36.)

Construction: stonepaste

The Met Museum brief description of the reference cup indicates it has been made of stonepaste. The extended catalogue entry on this sheds no light upon what stonepaste actually is nor does any similar article in the museum. This led me to believe ‘stonepaste’ was a common ceramic term. Prior to this project, I had never noticed ‘stonepaste’ or did not know how it was shaped. I was familiar with ‘earthenware’ which are essentially items made of clay/terracotta and fired at a low temperature. I'd also researched the development production of high temperature porcelain in China. I knew what stoneware was, compositionally different clays fired at high temperature, and the theory of slip casting but I had never noted ‘stonepaste’ before.

Stonepaste was originally developed by the Persian / Iranian potters to counter the lighter / stronger porcelain being created and exported by China. Porcelain has a kaolin clay base and fired at ~1350 degrees to create a fused, very light weight, thin, strong object. These items were a highly prized and traded commodity with some featuring in 16th century English portraits. The Persian potter’s response to this change in the market was to develop stonepaste (aka. fritware or faience) during the 12th century (Curatola 2006). Stonepaste combines frit (powdered quartz and a flux) with clay. The composition is generally stated as 10 parts silica (powdered quartz stone), 1 part clay and 1 part glass frit (quartz sand with a flux element). This recipe was documented by Abū'l-Qāsim, a 12th century Kashani (Iranian city in the north) who wrote a treatise on the ceramic industry (Allan 1973). The introduction of silica and quartz sand results in a stiffer clay material to work with but the item will vitrify at a lower temperature. The powdered silica melts and bond to create interlocking crystals during vitrification. This is what provides the strength to the object. The stronger the wall material, the thinner it can be. As heavy ingredients like clay and quartz were not transported great distances, the local type of glass frit and silica used in the stonepaste would modify the firing temperatures by 50-100 degrees (Mason & Tite 2007). The stiffer stonepaste could still be thrown on a wheel however Curatola (2006) suggests that molds could also be used to help create complicated shapes without overworking the material.

Construction: shape

Body

The reference cup appears to be a common shape for the time and area. I have collected a number of reference images of spatial and temporally similar cups in Table 1 but I'll summarise my findings here. Seven of the items (1-7) all demonstrate a similar body shape to the reference cup though they have a variety of green, transparent, lustre or multi-colour glaze. They all have a smallish foot, a bulbourous body and a small, upright lip. The smallest is 11cm and the tallest 17cm with reasonably similar proportions. While size does seem to dictate the label, cup vs jug, with some overlap, the overall shape remains the same.

The most significant item of note, item 8, an 8th century BCE cup, has a very similar shape suggesting this may have been regionally quite common for an extended period. As a side observation, all of the rounded items in the collection have the same, small vertical lip, except the 700-900 BCE cup.

I have included additional cups in the reference collection as it is important to note that this shape isn’t the only one utilised in the area with a beaker shape shown to be equally common in green (12, 10), transparent (11) and multicolour overglazed (9) as well.

Handle

The seven bulb shaped cups in the reference collection all have a small handle placed in the upper half of the form. Cups 1, 4 and 7, all have almost circular handles that are attached to the body of the cup on both sides. Cups 4 and 7 have an additional stabilizing bar which links the handle to the lip of the cup. This bar would strengthen the handle and allow the drinker to pick it up with a single finger, resting their thumb on the bar. Bars like this are ergonomic additions and reduce the strain on the holders wrist.

Cups 2, 3, 5 & 6 have a more tear drop shaped handle. This handle connects to the lip on the upper side and descends to connect to the main body in almost a straight line. It's possible these handles would accommodate two or more fingers. Handle wise, 5 & 6 seem to be the most similar to the reference cup even though there are a variety of handle types in use in this time and area.

Image 2. Cup with Floral Decoration detail. Chipped design on lip suggest the potential for slip scratching to create relief design.

Glaze - slip

"To paint a design under a glaze without the design running required a mastery of the medium that was attained only with much trial and error. This cup and the following dish are representative of another preliminary attempt at underglaze painting made by twelfth-century Persian potters. The body is covered with a thick layer of frit of the same composition but of a consistency different from that of the body. After drying, it is carved so that the design is left in relief. The object is then covered with a transparent glaze and fired.

This is a common shape within this group and the striped effect on the lower section as well as on the short neck is a popular device on this so-called silhouette ware.". (The Met Museum, Item number 1970.36. catalogue entry accessed 1/1/2020).

Casual reading of the reference cup’s catalogue entry would suggest that the cup has been dipped or covered in a runnier layer of stonepaste (presumably black) which has then been scraped off to create the design (scraffito-esk). Image 2 shows the detail along the reference cup's lip where small indentations in the black design may have been caused by careless application of a knife while scraping. The thin turquoise band above the upright black bars would most easily be created through scraping as leaving such a fine void in a glaze would be challenging during painted application.

Image 3. Cup with Floral Decoration detail. Repairs in cup rim are highlighted in light turquoise and grey. The black design elements do appear to be more prominent than the turquoise.

The scraping process would create a raised design in the black which would help retain the turquoise transparent glaze in the divoted areas.  The fact a majority of the flaked off turquoise is in central areas away from the black may support the scraffito glaze treatment. However, it is difficult to place much weight on the bulk glaze state of reference item as it has been broken in the past as demonstrated by the light turquoise and grey lines. The strain on the glaze when it broke reduces the evidentiary weight of the glaze condition. Image 3 shows areas where the black glaze does appear to be slightly more prominent than the turquoise. It is, however, difficult to tell if the grey ‘highlights’ are repairs or not. Examining whole cups similar to the reference cup (items 5&6), reveal the black designs are raised and more prominent than the turquoise glaze.  This also supports the suggestion a frit-drip and scraffito technique was utilised in the glazing process.

Image 4. Cup with Floral Decoration detail. Underglaze flecks in the turquoise glaze and perfectly uniform design edges

Additional supporting evidence for frit-dipping can be seen in Image 4, a magnification of a palmetto design element. The pink lines demonstrate how the two bottom sets of leaves on the palmetto perfectly match each other. This interlocking design is easily achieved through scraping a single layer of black off to create the leaf division. It would be significantly harder to achieve this feature by painting the frit on. The yellow arrow, points towards some small flecks of black within the turquoise indicating the scraping hasn't fully removed the frit.

A strong counter argument against frit-dipping are the large areas of turquoise that do not have any trace of black specks in them. If the frit coat were the same composition (with the addition of black oxide) as the body of the cup, the frit grains would be difficult to scrape off the main body of the form. From past experience, it is almost impossible to remove every speck of a dark glaze from a pale background. Instead, I would propose the design elements are painted on and then refined or cleaned up by scratching with a knife.

Glaze - underglaze

Image 5. Cup with Floral Decoration detail. Blebby design details suggest the black features have been painted on.

As can be seen in Image 5, the reference cup has a few small blebs on the palmetto vines. These appear randomly and do not seem to be intentional. Given their rounded shape, I would assert they occur when the palmetto design is painted onto the cup as a frit underglaze. The blebs are either drips, or the start/end of a brush stroke. Their small rounded shape would be difficult to deliberately achieve with a knife edge. The underglaze and scrape approach would have the benefit of saving time on scraping away significant areas of glaze required to clean up the areas that become turquoise.

Reference Cup Summary

The reference cup has been formed from a stiff, silica rich stonepaste. It may or may not have been formed with the assistance of a mold but the texts suggest stonepaste is still possible to throw. After bisque firing, the cup has had a dark grey or black underglaze applied to it. The design has been further refined by using a knife to scrape in finer detail. The whole cup is then dipped in a transparent turquoise glaze and fired for a second time.

My cup

There are seven main stages to constructing my cup; throwing the body, trimming the shape, attaching the handle, bisque firing, underglaze, overglaze and stoneware firing. The construction of the reference cup and my access to various resources have both controlled how I created my object. I’ll discuss my process in sequence with referral back to the reference cup construction for comparison.

Image 6. My cup – post bisque firing with the initial glaze pattern sketched on in greylead

Constructing the replica - stages and learning

1. Throwing

When I decided to make this object, I signed up for a 5 session class on wheel throwing at ClayMake Studio, a local ceramic focussed studio and school. Prior to this class, I’d thrown two bowls and a cup at Pennsic 2017 / 2019 and five olive bowls in a single once off class. In my first session I learned how to throw cups deliberately to achieve the shapes I was aiming for. I further refined this skill in the second session. To create this cup, I used a buff coloured clay that matched the base colour of the reference cup. The main drawback of this clay is it has the texture of butter. This means the walls of the cup need to be slightly thicker to achieve the same height as a more silica rich clay (i.e. stonepaste). The reference cup was 14cm high and 14.6cm wide and weighed 450.8 grams. I started with 500 grams of clay to account for 10-15% weight loss from the water content but probably should have started with 650gms. I threw the cup so it ended up being 9.5cm high. By down-scaling the shape, I was able to have thinner walls and achieve a bulb shape closer to the original.

2. Trimming

After the cup was thrown, I covered it in gladwrap to retain its internal moisture. The next week I turned it upside down on the wheel and trimmed off as much of the excess clay to emphasise the bulb shape. I may have been able to trim more but I’m still not familiar enough with the clay to be confidant I won’t collapse my shape. Some of the extant cups have the internal part of the foot trimmed out, reducing the weight of the base. There was no image of showing the bottom of the cup but the shape suggests a foot rim is common. I have not cut a rim into the base of the cup as I did not retain enough material to do so. As my first ever thrown bowl ended up forming a crack in the base, I am still quite cautious about ruining future objects.

3. Handle

Sessions 3 & 4 of the class was dedicated to making and attaching handles. I tried very hard to replicate the small tear drop shaped handle however I encountered an unexpected problem. Handles need to be attached to the body of the cup when both bits of clay have the same amount of water. If they dry out at different rates the handle will crack off the body. The two days I made handles were over 40 degrees. It was impossible to create a handle, dry it out sufficiently to retain the tight tear drop shape and not to end up with it being too dry to attach. I settled on making a more open shape which fit the more open lip better and would allow me to use two fingers to hold the cup. This shape can be a little wetter and saggier and therefore didn’t dry out before attachment. The handle shape is the biggest deviation between the reference cup and mine version.

4. Bisque firing

The cup was bisque fired to drive the moisture out and strengthen the cup prior to glazing.

Image 7. My cup. Partially underglazed cup.

Glazing the replica - stages and learning

5.     Underglaze

As outlined earlier, I believe the black design has been painted upon the reference cup then the details have been cleaned up with a knife. I have followed this technique which has reduced the amount of clean-up of excess black oxide that is required. Image 7 was taken prior to clean up. It’s possible to see little blebs similar to those on the reference cup. All of the little blebs, mistakes and areas where the turquoise will be too thin were quickly addressed by scraping them off with a knife (Image 8).

6.     Overglaze

The foot of the cup has been sealed in wax to prevent the glaze melting onto the kiln shelf. The cup will be dipped in a transparent turquoise-green overglaze. This is scheduled for the 13^th when ClayMake Studio reopens.

Image 8. Underglaze. Bottom – post underglaze painting, Top – post knife cleanup

7.     Firing

The cup will be fired to stoneware temperatures ~1300 Celsius. Mason and Tites (2007) suggest stonepaste would have been fired between 1000 and 1100 Celsius. The flux and frit reducing the temperature at which particles start to melt and interlock. As I don’t own a kiln and am using ClayMake Studios firing service I have no control over the temperature utilised I would like to experiment with stonepaste creation in the future but for now the stoneware firing temperature should achieve a similar strength.


Edit: the cup was dipped in opaque sea green glaze followed by transparent green and fired to ~1250 degrees.

Image 9: the completed cup. So very very happy with this!

Reflection

Prior to this project, my approach to creating a glazed object would have been to visit a glaze-it yourself venue, buy pre-made bisque and use their pallet of provided underglazes for the design. This meant I was never in control of the shape or the colour choices I had. These restrictions were frustrating. I’m glad I undertook to learn how to throw pots. In addition to learning a new craft, I learned a lot about stonepaste. I was familiar with earthenware, and porcelain but had never encountered fritware/stonepaste.  I had a steep learning curve to achieve the bulb shape. While I have not yet mastered throwing this shape of cup yet nor making handles but I am quite happy with the item I created. It looks very similar to the reference cup even though the handle couldn’t be formed properly. The glazing so far has been successful and I am eagerly looking forward to ClayMake reopening so the cup can have a final fire.

Key references:

Allan, J.W. (1973), "Abū'l-Qāsim's treatise on ceramic, Iran (journal), 11: 111–120, JSTOR 430048

Curatola, G (2006). Persian Ceramics from the 9th to the 14th century. Edited by . 2006. Book. ISBN-10 88-7624-750-5

MASON, R. & Tite, M.s. (2007). The beginnings of Islamic stonepaste technology. Archaeometry. 36. 77 - 91. 10.1111/j.1475-4754.1994.tb01066.x. 

The Met Museum. Accession No. 1970.36. The extant item and catalogue entry. https://www.metmuseum.org/art/collection/search/452082 Website accessed 1/1/2020

Reference images can be found here.