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Home , Ball clay, Clay, Fire clay, Kaolinite, Marine clay

An Analysis of Naturally Derived Marine as a Medium

Julienne E. Beblo University of North Carolina Wilmington Faculty Mentor: Aaron Wilcox University of North Carolina Wilmington

Abstract This project was conducted to evaluate the use of as a ceramic medium. Samples of the clay were collected from Kure and analyzed using workability tests, mineralogi- cal analysis, and a chemical analysis. The clay shrank 15.63% after air drying and 17.75% after being fi red. was 26.0% and plasticity was identifi ed by handling the material. It contained 27.43% , 55.08% , 1.06% clay and also had high concentrations of aluminum and . Organic content was 15.79%. The marine clay did exhibit plasticity, was able to be thrown on a wheel and withstood fi ring. However, the small amount of actual clay present made the material more diffi cult to control and even after fi ring, it maintained a certain degree of fragility. The plasticity is likely a result of the high organic content. The clay is not ideal for functional studio work but it can perform as a ceramic medium.

eramic clay has been widely used and those are defi ned, and what properties of the Cstudied for thousands of years. As a collected material infl uenced its usability in result, there is a comprehensive understand- the ceramic studio. The composition of the ing of the material and standards for evalu- collected material was analyzed and its func- ating its potential as a functional ceramic tionality was evaluated using existing stan- medium. But even as these standards are dards in ceramic studio practice. currently used, the fi eld continues to change as new processes are utilized and the materi- Defi nitions of Clay als are pushed to new extremes. In addition, much of the ceramic making process is still Clay is a naturally formed material derived determined by the preferences of the potter. from . Interestingly, clay can The purpose of this project was to examine refer both to a particle size and to specifi c the use of naturally derived marine clay as compositions of natural materials. Any sedi- a ceramic medium. It predominantly en- mentary particle that is <2μm is considered compassed the production of creative pieces, clay. In addition, clay are defi ned but with an emphasis on understanding the by their similar crystal structures and range characteristics of the collected clay, how of chemical compositions. Because of the

7 Explorations | Art and Humanities small particle sizes and chemical composi- clay similarly exhibits coarse particles and tion of clay minerals, the material exhibits organic-rich content. certain properties that have made it useful Marine and aquatic clays are also known in . Clay particles have a strong af- to create clay balls. These sedimentary for- fi nity for water and when the two substances mations occur when the fi ne particles of clay combine, the material swells. This helps the suspended in the liquid are rolled back and particles remain adhered to one another and forth due to wave and current action. The gives them the ability to retain a stable form particles naturally adhere to one another when wet. , for example, is a com- when water is present so the formation can mon clay . It has a two-layered, hex- become signifi cant, forming lumps or balls of agonal shape with a diameter ranging from material. These formations will occasionally 0.3 μm-0.01 mm and a general thickness of roll up on shore and often exhibit relatively 0.05 μm. This particular structure has a high homogenous contents. surface area that is able to interact with water Generally, any kind of raw clay used in . The interaction between water the studio can be categorized into fi ve dif- and clay particles actually gives the material ferent groups: clay, , fi re clay, the characteristics that make it usable as a ce- clay, and surface clay. China clay ramic medium. is formed at the base of mountains and has A clay’s origin and whether it has been minimal impurities. It is rare, exhibits mini- transported from the spot in which it formed mal plasticity, and is also the most , affect its properties. Clays that are found at or resistant to heat. Ball clay exhibits the their origin are considered “residual” while highest plasticity and has always been moved those that have been moved by natural by water from its primary spot of formation. forces-water, wind, , etc.- to another This sedimentary clay has a fi ner particle size depositional area are considered “sedimen- that results in a high amount of shrinkage. tary.” Transportation of sedimentary clays Fire clay is found in mountain or desert areas increases the potential amount of impurities and has varying, coarse particle sizes. It is a present. This difference in composition may strong clay that has good standing strength change the plasticity and color of the ma- and is usually colored beige, red, gold, or terial. A high level of organic matter also red-brown when fi red. Stoneware exhibits tends to increase plasticity and occasionally properties similar to both ball and fi re clay. the stickiness of a clay. These characteristics make it a very work- Marine clays are likely the most common able material that also fi res to a high density. source of sedimentary clay. Generally, they Surface clay is the most prevalent. Because form when fi ne clay particles found in fresh- it has experienced years of movement, the water systems are deposited in brackish wa- level of impurities is high which increases ter. The clay particles absorb various impuri- the workability of the material. It tends to ties as they are transported from their place fi re a -red color, but this can change de- of origin by water movement. Marine clays, pending upon the presence of various metal- like most sedimentary clays, exhibit a higher lic oxides. Surface clay is also the material level of homogeneity and tend to have a high most commonly used by indigenous cultures percentage of organic content. They can be to create ceramic ware. grouped into three different categories based Raw clay exhibitis characteristics that are upon their location in various . indicative of its origin and its qualities when Pelagic clay is found in deep water and tends wet. The creative process, however, usually to have very fi ne particles. Littoral clay is involves additional steps such as fi ring and found between the high and low watermarks glazing. Fired clay becomes ceramic ware of a shore and contains coarse particles with a and it exhibits specifi c properties that infl u- high percentage of organic matter. Estuarine ence its utility and its aesthetic. Ceramic

8 Julienne E. Beblo ware is generally categorized into three sepa- estimate the size at which the piece needs to rate groups. is very porous and be created when wet so as to be the desired lightweight. It fi res at a low size after being fi red and glazed. range and has commonly been used among Porosity refers to the percentage of empty tribal societies. It will absorb 10-15% of its space, called pores, found in the material. unglazed weight in water. Stoneware is a This characteristic is important because the very hard and durable clay that holds liquids number and size of pore spaces infl uence the and is not easily broken. It will absorb 2-5% hardness of the clay and its ability to vitrify. of its unglazed weight in water. is Porosity can also be indicative of the type a dense and vitreous clay. It is known for of clay body being used. Porcelain clay has its generally white color and translucency. It 0-3% porosity while stoneware has 1-6% and will absorb 0-1% of its unglazed weight in earthenware has 4-10%. Measuring porosity water. Since the collected material was as- is diffi cult because some of the pore spaces sessed as a ceramic medium, understanding are sealed within the clay. To overcome this the categorization of clay and ceramic ware obstacle, testing the percentage of water ab- was necessary for describing the collected sorption is one of the most common meth- clay and for comparing it to other clays com- ods for testing porosity. This measures the monly used in the studio. amount of water absorbed by a bisque-fi red piece of clay. There are multiple procedures, Workability Defi nitions including some that require the bisque-fi red clay to be boiled for various time periods and The quality of clay used in the studio is a others that soak the clay overnight. somewhat ambiguous characteristic that can- Plasticity is an interesting characteristic of not always be easily identifi ed. Most often clay because there is no quantifi able measure- it is based upon a potter’s specifi c prefer- ment for it. Although potters will generally ence or upon the qualities needed to produce agree that plasticity is an important character- a particular piece of work. Even so, certain istic, it is predominantly determined by a pot- properties have been identifi ed that generally ter’s preference. Even so, there are multiple indicate the workability of clay when used in methods to determine if it is present. Simply a studio setting. Fortunately, most of those working with the clay to assess if it can with- have been given a quantifi able method of stand , stretching, and a combination measurement. Shrinkage, porosity, and plas- of the two while still maintaining its shape ticity are three of the most common charac- and without tearing are observed characteris- teristics used to determine the workability of tics that are indicative of plasticity. A very a clay body. simple method for identifying the presence of Shrinkage is a natural process that occurs plasticity is known as the coil test, a process as the clay dries, or as it is bisque-fi red and in which a pencil-sized coil of clay is looped. glaze-fi red. It is also an easy characteristic If the clay remains smooth, it has good plas- to measure. Clay at the desired plasticity is ticity. However, if excessive cracks appear rolled out into a slab, a measurable block is in the bent coil, there is likely very little from the slab and then its length is re- plasticity. In addition, if the clay is unable to corded. The length of the block is then re- maintain a tall form, and it begins to fold into measured after drying and again after being itself and sag, the material has low plasticity. fi red. Using these measurements, the percent Sometimes the percent of water present when of shrinkage can be calculated. Although this the sample is at the desired plasticity is used characteristic does not necessarily defi ne the as a quantifi able method of judging plasticity. quality of a clay, it is an important property Again this measurement, although quantifi - of which to be aware. Understanding how able, is still based upon a potter’s defi nition much the material shrinks allows a potter to of the appropriate plasticity.

9 Explorations | Art and Humanities

Firing and Glazing temperature, one at the desired temperature, and one above the desired temperature-are Another desirable characteristic of clay is placed upright together, in ascending order of its ability to be fi red. Air drying clay does melting temperature, on a coil of clay. This not make it durable which eliminates its is known as a cone pack and it is then placed functionality. Firing clay to the appropriate inside the in an area that is visible to the temperature hardens the material and makes potter during fi ring. The cones are monitored the clay body a permanent substance. Once throughout the fi ring process and indicate fi red, clay is transformed into a more resis- when the temperature is approaching, has tant substance. Although it can fragment, the reached, or has passed the desired value. fi red material will remain in an unchanged state for thousands of years. CREATIVE PROCESS AND PURPOSE Firing can allow ceramic ware to reach a state of vitrifi cation. This is the point at The used for this project which the clay material becomes very hard was found and collected along the ocean and dense. As the temperature increases, water’s edge, predominantly deposited in components within the clay begin to melt and small clumps or balls that were embedded in fi ll in exterior pores on the clay. This process or resting on the sand. This specifi c mate- creates a durable and permanent substance. rial was collected because it shared a similar Further heating beyond the point of vitrifi ca- tactile quality to that of the stoneware clay tion, however, can lead to complete melting commonly used in ceramic studios. When and therefore the destruction of the utility of handled, the particles remained adhered to the clay. one another, they did not crumble, and the The use of to achieve this state of vit- appearance was smooth. The material had rifi cation and to add glazes was fi rst used by a dark brownish-grey color and was very the Chinese. Kilns allow fi ring to occur in a sticky. Its texture was rougher than the stu- semi-closed system in which temperature and dio clay, but it and resembled the consistency duration of fi ring can be controlled and moni- of raku clay. tored. The high remove water Initially, the clay was found on a barrier from the clay body, including those mol- , but a majority of the material used ecules chemically combined with alumina for the project was gathered from the shore and silica. Kilns must have a heat source at the end of Kure Beach, North Carolina. It that is able to transfer its energy to the clay was collected over several trips throughout pieces. The heat needs to be contained in the summer months. Samples were collected some way so that it is focused on the . in bags and then stored in a 5-gallon This system allows for the clay to be in an bucket to retain their moisture and to ensure enclosed and somewhat controlled environ- that no other materials would be introduced. ment that reaches the necessary temperatures In addition, a bottle of salt water was col- for vitrifi cation. lected from the same area to be used during Temperatures can be measured in a kiln by the working and throwing process in the stu- observing the reaction of pyrometric cones. dio. Because clay particles will easily absorb These pyramidal indicators serve as a physi- impurities from their surroundings, using salt cal representation of the temperatures within water from the location of collection helped the kiln. Their compositions of glaze-like to replicate an environment similar to where materials are designed to melt at specifi c the clay was found. In addition, it maintained temperatures. They have been standardized the salinity of the material which affected to range from cone 020-15, or temperatures the clay throughout the working and fi ring between 635ºC-1430ºC. Usually, mul- process. tiple cones-including one below the desired Although the use of clay is often infl uenced

10 Julienne E. Beblo by the preference of the potter, there are still there was no stratifi cation evident, it was an standards used to defi ne the workability of effective method of monitoring the settling of the material in a studio based upon some clay particles. In addition, it permitted obser- general properties. Using these basic char- vation of coloration and residues that formed acteristics of porosity, plasticity, shrinkage, in conjunction with the settling of the mate- and the ability to be fi red, the collected clay rial. Despite the fi ltration, there were still was evaluated to assess if it could perform as small shells and pieces of debris present in functional ceramic ware. the clay, although not nearly as many as had been present before fi ltration. METHODOLOGY Workability Tests The collected clay was fi rst fi ltered using a settling method in order to remove any de- Shrinkage was measured using the bris. All of the clay was placed in a 10 gal- equation: lon aquarium, which was then fi lled with salt water collected from the same area as the % shrinkage = (lengthwet - lengthdry)/ clay. The salt water and the collected clay (lengthwet) x 100 were thoroughly mixed in the aquarium, cre- ating a slurry of material. It was covered and Ten blocks were cut out of a slab of the col- allowed to settle for four weeks. The clear lected clay when it was at the desired wet- walls of the fi sh tank allowed the separation ness. Each block measured 8 inches in length between clay and water to be easily viewed. and 1 inch in width. They were each marked Once a clear layer of water had formed at to show inches and half-inches. Once the the top, it was siphoned off using a blocks had fully dried, one of them was mea- baster which minimized the amount of clay sured and its length was used to determine particles being collected along with the wa- the amount of shrinkage. It was bisque fi red ter. This siphoning was repeated until water and then measured again to determine the no longer appeared on top of the clay. The shrinkage after fi ring. clay was then allowed to dry to a workable consistency. Only the top layers of clay, those %LDS (after air drying) = (8.0 in – 6.7496 that did not contain the larger debris, were re- in)/(8.0 in) x 100 = 15.63% moved and placed in a 5-gallon bucket so as to maintain their moisture content. %LDS (after bisque fi ring) = (8.0 in - 6.58 The intent of the fi ltration method was to in)/(8.0 in) x 100 = 17.75% allow the clay to settle and stratify into lay- ers based upon the weight of the particles and The linear drying shrinkage (%LDS) after to remove any excess debris which would air drying resulted in a 15.63% reduction in have settled on the bottom. Even after four length while the %LDS after bisque-fi ring re- weeks of settling, however, there was no evi- sulted in a 17.75% reduction in length. dent stratifi cation in the clay. Large pieces Porosity was measured using the equation: of shell and other natural debris did settle out to the bottom but smaller shells and debris P = (weightsoaked - weightfi red)/(weight- still remained in the upper levels of the ma- fi red) x 100 terial. In addition, there was a rust-colored residue evident on the inside of the tank. It To measure porosity, a fragment of the potentially indicated the presence of iron in bisque-fi red collected clay was weighed. It the collected clay. was also weighed inside a plastic container Use of the aquarium was an innovative with a lid that was later used for transport. addition to the fi ltration process. Although The piece was boiled for fi ve hours and then

11 Explorations | Art and Humanities allowed to cool in the water. It was removed shape and exhibited plasticity. A sponge was and then the surface water was gently re- used to help eliminate continuous contact moved. It was placed back in the plastic con- with the rough clay. It also helped to keep tainer and covered to retain all of the mois- the outer consistency of the clay smooth. ture during transport. Then it was reweighed. There were a few particular characteristics that differed from the studio clay. One piece P = (12.40g - 9.84g)/(9.84g) x 100 = 26.0% was thrown too thin on the bottom curve. Rather than sag, as would have been expected The porosity (P) of the collected clay, with the stoneware studio clay, as the weight which basically equals the amount of water of the top of the piece pushed down it cre- absorbed, was calculated to be 26.0%. ated a vertical split in the bottom wall of the Because there is no quantifi able test for pot while the rest of the piece maintained its plasticity, the clay was handled and observa- form. This reaction could be attributed to the tions were made about its reaction. The coil combination of the stickiness of the clay and test was performed to check for cracking. its larger particles. The stickiness from the The clay was also compressed and stretched high organic content of the material helped to analyze its reaction. In addition, it was to keep it together. As excess weight pushed thrown on the wheel to see how the down on the clay, however, the organic mate- material retained its shape and if it exhibited rial could no longer hold the larger particles signs of sagging. As a fi nal, although less in- easily and a tear would form. The collected dicative test, the percentage water of plastic- clay forms also adhered more strongly to the ity (%WP) was measured using the equation: wheel than the studio clay. Again, this could be a result of the increased stickiness due to a %WP = (weightwet - weightdry)/ high organic content. (weightdry) x 100 Strangely, once the pieces had been thrown and were ready to be moved off of the wheel, The clay did exhibit plasticity. For the coil they maintained their intended form despite test, the material looped easily and minimal having to be removed more forcibly. This is cracking was evident. Simply handling the unexpected because the studio clay deforms clay revealed that it could withstand a cer- easily if too much pressure is applied when tain amount of stretching and compression. being removed from the wheel. The col- While throwing on the wheel, the pieces lected clay, however, compressed as it was rarely exhibited any signs of sagging and the being removed and then returned to its origi- clay maintained its form and height. nal form without showing any major signs of malformation. This elastic-like reaction is %WP = (13.30g - 8.84g)/(8.84g) x 100 = probably a result of the high concentration of 50.45% salt and organic matter.

The percentage water of plasticity (%WP) Mineralogical Analysis for clay that had reached the desired level of plasticity was 50.45%. X-ray diffraction (XRD) is used to deter- In addition to the workability tests, the col- mine the mineralogical composition in sedi- lected clay was used in the studio to assess ments. It is used for identifi ca- its throwing capabilities and tactile quali- tion because the particle size is very small, ties. The material was able to be thrown on generally falling between 1 and 10μm. In the wheel and multiple vessels were created. order for the collected material to be ana- Although the clay’s consistency was rough lyzed by XRD, a wet bulk sample was dried and contained more grit, it still maintained its at 110ºC for 24 hours to remove the moisture

12 Julienne E. Beblo and was then crushed into a fi ne with due to analysis. The major components mortar and pestle. The dried powder was within the material were quartz, kaolinite, na- treated for contained organic matter (OM) crite, and (Figure 2). All of those by applying a 6% Sodium Hypochlorite solu- were present in the clay particle fraction. The tion, buffered to pH 9.5 with 10% HCl. The sample contained 3.08% organic matter and treated sample was then heated in a water carbonate material. bath for 15 minutes to increase the reactivity of the oxidizer, centrifuged and the superna- Chemical Analysis tant decanted. The treatment was repeated until the OM was entirely removed. Samples of the collected clay were dried For carbonate removal, the sample was and crushed. A mass of 0.2 g of the dry ma- washed in an anhydrous Acetic Acid – terial was measured out into three separate Sodium Acetate solution. It was then heated Tefl on digestion vessels and a fourth was in an 80°C water bath to increase reactiv- left empty as a blank. Volumes of 1.2 mL of ity and the supernatant discharged after concentrated HCl and 3.8 mL of concentrated centrifugation. HNO3 (both trace metal ) were added to After this chemical alteration, the sample the 4 digestion vessels. All four vessels were was wet sieved with a 125 screen (64μm) to sealed and placed in pressure-safe frames remove the sand particle size fraction. The and microwave digested for 50 min under remaining wet sample was dispersed in a so- increasing pressure and temperature (up to dium hexametaphosphate solution and fur- 150 psi and 210°C) using a CEM MARS mi- ther mixed in an ultrasonic bath. This stimu- crowave digestion instrument. After cooling, lated sample was then settled out, applying the samples were fi ltered and brought to 50.0 Stokes Law for settling particles. After the mL with high purity water. Samples were an- allotted time interval, it was decanted to sep- alyzed for metals using inductively coupled arate the silt particle size fraction from the plasma optical emission spectrometry on a clay particle size fraction. Both fractions Perkin-Elmer Optima 2100 DV instrument were centrifuged, washed with distilled wa- that was calibrated using -matched ter and after all the dispersant was removed, mixed metal standard solutions. dried in an oven at 70°C. The fi nalized sam- As the samples were being fi ltered, the liq- ples were mounted on aluminum discs and uid in each vessel displayed a different hue analyzed using the Rigaku Minifl ex II X-ray of yellow. The within each sample Diffractometer. also appeared to be three different colors. This entire procedure was repeated with a This is unexpected because each of the sam- sample of the clay used in the studio. Having ples was taken from the same bulk sample. both clays sampled the same way allowed There were no intentional differences be- for a precise comparison of composition be- tween samples when they were collected. tween the two. The concentrations of the metals in each The collected material had a particle size solution were measured by the microwave distribution of 27.43% sand, 55.08% silt and digestion instrument. Those concentrations 1.06% clay with a loss of 0.64% due to the were then multiplied by the volume of the analysis. The major mineralogical compo- solution and divided by the sample weight nent within the material was quartz. The clay to calculate the concentration (μg/g) of each mineral, kaolinite was present and there was metal in the dry samples of collected clay. a trace of (Figure 1). The Iron and aluminum had the highest concen- sample also contained 15.79% of organic ma- trations in the samples and levels of cobalt terial and carbonate material. and cadmium were BD, or below detection For comparison, the studio clay had a par- (Table 1). ticle size distribution of 1.76% sand, 90.39% silt and 4.67% of clay with a loss of 0.10%

13 Explorations | Art and Humanities

KILN CONSTRUCTION AND FIRING the progress of the cones and as a for PROCEDURE removing the drawrings while the kiln was being fi red. An insulation was used to Initially, the blocks of collected clay used block the opening when it was not in use. for shrinkage testing were also bisque fi red The gas burner was placed parallel to the along with the studio ware in one of the stu- specifi ed opening. It was attached to the dio kilns. Because the bisque fi ring only main gas line through a series of pipes. Each reaches temperatures up to cone 06 (1830ºF), joint between pipes was wrapped with tape this gave a general indication if the mate- to form a tighter seal and then securely fas- rial could withstand lower fi ring. A single, tened. To ensure proper sealing, dish soap bisque-fi red block was then placed-unglazed- was dripped onto each joint as the gas was in the studio kiln along with studio ware that running. Any bubble formation would have was being glaze-fi red. The glaze kiln fi res up indicated a gas leak. to cone 10 (2381ºF), so this gave a general in- The ceramic pieces made of the collected dication of the material’s ability to withstand material, the cone packs, and the drawrings higher temperatures. were placed on the interior shelf of the kiln. After the initial bisque fi ring in the studio The drawrings were positioned in a row di- kiln, the sample blocks of collected material rectly in front of the spy hole so that they became a brick-red color. They were very could easily be retrieved using a piece of re- light weight, but also they crumbled and bar. The cone packs were positioned so that broke apart easily. The block that had been they could be easily seen through the spy placed in the glaze fi ring along with the stu- hole. The pottery was then spaced through- dio ware melted, bubbled, and then adhered out the rest of the kiln. to the piece of kiln shelf on which it had been Two fl at kiln shelves were placed on top of placed. Although the block maintained its the kiln to contain the heat. A gap of about general shape, it became hard and lumpy. It 1.5 inches was left between the pieces to also had a metallic grey and rust color when serve as a damper. Once the interior shelf it was removed. had been organized and the top of the kiln A small kiln was then constructed to allow positioned, the gas was turned on. It was for the collected material to be fi red sepa- adjusted periodically, usually every hour, to rately from the studio clay (Figure 3). Cone increase the heat and the area of fan exposed packs-made of cones 09, 08, 06, 04, 6, 8, 9, was adjusted accordingly to allow for the and 10-were placed on the kiln shelf along amount of air fl ow needed to keep the fl ame with the ceramic pieces to serve as an indica- burning. Temperature was monitored occa- tion of the temperature in the kiln. In addi- sionally with a pyrometer but the cone packs tion, drawrings of the collected material were served as the main indicator of temperature. made in order to monitor the effects of fi ring One drawring was taken out periodically on the clay. Drawrings are small loops of the to check the condition of the clay. It was re- clay that can stand vertically in the kiln so moved through the spy hole with a piece of that they can easily and quickly be removed rebar and then submerged in a bucket of wa- in order to monitor the material as it is being ter for rapid cooling. This allowed it to be ex- fi red. The creation of the smaller kiln permit- amined almost immediately and was repeated ted more control over the temperature of the three times during the fi rst fi ring. When the kiln and the ability to remove the drawrings drawring that had reached maturation had during the fi ring process. been removed and cooled, the gas was turned The kiln was constructed out of fi rebricks off and the kiln was allowed to cool. The fi rst on a base of cinder blocks. An opening be- fi ring in the small kiln, from ignition to turn- low the interior shelf allowed access for the ing off the gas lasted 3.5 hours. gas-fueled fl ame which heated the kiln. An The three pieces fi red initially in the kiln additional opening was created level with the interior shelf. It served as a spy hole to check

14 Julienne E. Beblo built specifi cally for this project also melted It is important to take note of some over- (Figure 4). The taller piece sagged and col- all observations through the drying and fi r- lapsed into itself while the shorter pieces just ing process. After air drying, all pieces of the melted down on themselves. The same shiny collected clay remained a dark grey color but black, speckled glaze that formed on the lat- had also formed a white residue (Figure 6). ter draw rings was evident on the pieces. This residue is likely salt that formed as the Interestingly, although the glaze did form on water evaporated, causing the salt crystals to the outside of the pieces, the brick red color precipitate on the surface of the piece. Once was still maintained on the interior and un- bisque-fi red, the collected material exhib- derside of the pieces, albeit a darker shade. ited a signifi cant amount of shrinkage and its In addition, there was a strange smell emitted color changed from a dark grey to a brick red. from the kiln, however, it went away as fi ring It remained lightweight but was not particu- continued. larly durable. The single block that was also The process was repeated a second time glaze-fi red with the studio ware melted. with some minor adjustments made based For the fi rst fi ring in the small kiln, the upon the initial outcome. In an effort to reach pieces melted, although the progression of vitrifi cation without causing melting, the kiln drawrings did indicate vitrifi cation had been was only allowed to run until cone 04 have achieved. Even so, the shiny smooth sur- fallen but cone 6 was still standing. At this face that formed with vitrifi cation revealed a time, the pieces exhibited a shiny surface but natural fi lm of glaze. The pieces in the sec- also were still maintaining their form. Five ond fi ring of the small kiln did not melt, but drawrings were used in the second fi ring their appearance was different from those in to allow for additional chances to monitor the fi rst fi ring. These, too, exhibited a thin progress. The fi ring, from ignition to turn- fi lm of natural glaze although the texture was ing off the gas, lasted about 4.5 hours. The much rougher and the coloring was different. additional hour needed for fi ring likely oc- The natural glaze was likely a result of the curred because of the manual control of the salt precipitating on the surface of the pottery. gas burner. The gas was probably increased more slowly than the fi rst fi ring, thereby the DISCUSSION temperature increased more slowly. During the second fi ring in the small kiln, The collected clay is sedimentary because a similar smell was emitted, but that time is it has been moved from its spot of origin was more pronounced and lasted a bit lon- and has picked up a number of impurities. ger. It is likely that this smell was caused Because it was found on the ocean shore be- by the burning off of organic material. Once tween the high and low tide marks and con- the material had been removed, the smell tained a high level of organic matter, the ma- dissipated. In addition, the pilot burner was terial would be considered littoral clay when releasing a lot of fl ame, more than what was categorizing it based on marine clays. In ad- usually seen, but there was no way to adjust dition, due to its low fi ring temperatures and it. The second set of pieces did vitrify and did the brick-red color it becomes after bisque- not melt. They had a glassy surface and were fi ring, the material is likely surface clay. This much more durable. They also were able to is further supported in that surface clay has a hold water without leakage. However, the high level of impurities and is the most com- texture was rougher and the coloring exhib- mon kind of clay found. ited more reds and even some yellow while The high level of quartz found in the marine the fi rst coloring was predominantly a dark clay also had a large impact on the quality of grey (Figure 5). In addition, when the pieces the material as a ceramic medium. Quartz is were removed from the kiln, they had an odor a free state of silica, which is a common com- similar to that of the wet material. ponent found in clay. The presence of quartz

15 Explorations | Art and Humanities can reduce plasticity, lower refractory ability, found in the marine collected clay. In general, and limit the crushing and tensile strength these tend to increase the plasticity of a clay of the clay. Sedimentary clay, in particular, body. Although the collected material did tends to have a high concentration of quartz. exhibit plasticity, kaolinite and montmoril- The low fi ring capabilities and fragility of the lonite were found at such low levels that it pieces, even after fi ring, are all possible ef- is unlikely they signifi cantly infl uenced the fects of the high quartz concentration. overall plasticity. It is most probable that Kaolinite and montmorillonite were both the plasticity was a result of the high organic Figure 1: XRD compilation scan of collected clay

Figure shows the XRD peaks indicative of the presence of Quartz (Q), Kaolinite (K), and Montmorillonite (M).

Figure 2: XRD compilation scan of studio clay

Figure shows the XRD peaks indicative of the presence of Quartz (Q), Kaolinite (K), and Halloysite (H).

16 Julienne E. Beblo content, which is known to have a signifi cant the minimal percentage of actual clay made effect on this characteristic. the material more diffi cult to control. More Chemical analysis revealed that there were than likely, the signifi cant plasticity was a high concentrations of aluminum and iron in result of the high amount of organic matter the marine clay samples. Aluminum, in the in the material. Once fi red, and when not form of alumina (Al(OH)3), may reduce the melted, the pieces were roughly textured plasticity and increase the refractory abilities and did not show a consistent coloring. of a clay. Iron, not surprisingly, can affect the They were also porous and still maintained color of the material, often producing red or a certain degree of fragility. Both of these brick-colored clay. In addition, it may form characteristics make the material unsuitable a scum on the fi red ceramic ware and reduce for storing food or liquids. Even so, the col- the refractory abilities of the clay. The red lected ocean clay did function as a ceramic color of the bisque-fi red clay and its low fi r- medium and the vessels created possessed a ing temperature were likely affected by the unique and aesthetially pleasing quality. high concentration of iron. The aluminum may have decreased plasticity; it does not, ACKNOWLEDGMENTS however, appear to have had any additional effects on the material. I would like to thank my advisor, Professor Aaron Wilcox for his guidance and support CONCLUSIONS of this project. I would also like to thank my Honors Committee members, Dr. Nicholas Ultimately, the collected marine clay did Hudson, Dr. Michael Smith, Dr. Sridhar not perform ideally in the studio. It did ex- Varadarajan, and Dr. Diana Pasulka, for their hibit several properties characteristic of clay, advice and guidance. A special thanks, as including critical plasticity. These properties well, to Thorger Gabriel Enge for his work did allow the clay to be thrown on the wheel, on the mineralogical analysis, Dr. Skrabal for creating the shape of functional vessels. It his work on the chemical analysis, and the was able to withstand lower fi ring and it vit- Art and Art History Department. This proj- rifi ed and hardened to a more durable state. ect would not have been possible without the Even so, the excessive amount of sand and help of these people and I am so appreciative of their time and support.

Table 1: Summary of chemical analysis results

17 Explorations | Art and Humanities

Figure 3: Image of melted pieces after fi rst fi ring

Figure 4: Image of small kiln built for fi ring the collected clay

18 Julienne E. Beblo

Figure 5: Image of vitrifi ed pieces after second fi ring

Figure 6: Image of dry, collected clay showing evidence of salt precipitation on the surface

19 Explorations | Art and Humanities

References

Chen, Pei-Yuan, “Table of Key Lines in X-ray Powder diffraction Patterns of Minerals in Clays and Associated Rocks,” Department of Natural Resources Geological Survey Occasional 21(1977).

Foley, Nora K., “Environmental Characteristics of Clays and Clay Mineral Deposits,” U.S. Geological Survey, accessed February 4, 2013, http:/ pubs.usgs.gov/info/clays.

Grimshaw, Rex W., The Chemistry and Physics of Clays and Allied Ceramic Materials, 4th Ed. (New York: Wiley-Interscience Division, 1971).

Haas, William H., “Formation of Clay Balls,” The Journal of 35 No. 2 (1927).

Nelson, Glenn C., Ceramics: A Potter’s Handbook, 5th ed., (New York: CBS College Publishing, 1984).

Peterson, Susan and Jan Peterson, Working with Clay, 3rd Ed., (New Jersey: Pearson Education, Inc., 2009).

Rhodes, Daniel, Clay and Glazes for the Potter, (Radnor, PA: Chilton Book Company, 1957).

Rice, Prudence R., Pottery Analysis: A Sourcebook. (Chicago: The University of Chicago Press, 1987).

Rice, Prudence R., ed., The Prehistory & History of Ceramic Kilns (The American Ceramic Society, 1997).

Worrall, W.E., Clays and Ceramic Raw Materials (New York: Halstead Press, 1975).

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