By Jerry Bennett
I have been thinking recently about the importance of working with ceramics and how, time after time, I have been influenced by old traditional techniques in the craft. I find it ironic that I have found major influence in the traditions of pit-firing, and recently the use of paperclay. Paperclay has many advantages for the modern clay artist including; increased pre-firing strength, reduction in warping, increased joining capacity in both wet-to-wet joints and dry-to-dry joining. Paperclay has made a whole array of techniques available to me that I could not have thought of even a year ago. Super thin building techniques, translucent porcelain, and a very fast working style are all of the opportunities I have experienced. Here are some of the things I have learned along the way:
The method described below uses handheld power tools and ceramic production equipment. Use caution when using all equipment in the studio. The mixer spins at high speed and you should always keep your hands out of the bucket when mixing clay. Follow directions printed on the tools and read the operation manual. When mixing dry ingredients such as the paper or clay, wear a dust mask)). When firing paperclay in a kiln, make sure adequate ventilation is provided to prevent breathing kiln emissions. For your safety read all safety publications concerning materials you are using. Do not use moldy (Black) paper clay.
Paperclay can be made out of any clay an artist would want to use. Generally speaking, the more refined the clay the more benefit there is to adding paper fibers to the clay. The benefits to porcelain having paper fibers are very pronounced, lesser for stoneware and almost none for earthenware. Commercially paperclay is used to retard warping in clay, reduce weight of clay objects, and to lessen the cost of producing clay objects by replacing part of the clay with paper fibers which costs less. This is a common practice in the brick making industry.
If you use cellulose insulation as your source of paper fiber (recommended), use a clay formula designed for a higher temperature for firing. I fire porcelain to cone 6. I use Standard porcelain #257 which is rated for cone 8-10. Cellulose, which is actually just ground up newspaper, contains borax and boron which is used to reduce the fire hazard for the installed cellulose ceiling insulation. The Borax acts as a flux in the fired clay and has a tendency to reduce the maturity point of the fired clay. I have found that this can be a problem in ultra thin porcelain, and tall small based vases, that result in slumping of the clay form. This is less of a problem if you use stoneware or earthenware clay.
Paperclay is at its best when the paper fibers are equally disbursed into the clay mixture. Many commercial companies mix pug-milled clay with paper fibers. I feel this is not the optimum way to make paperclay. But, clay mixers such as Blue Bird and Soldner clay mixers can be used. To get a better mix of the fibers within the clay, a wet (slurry) mixture of clay works best. I use bagged moist clay and mix the moist clay with additional water until it is thick as yogurt. This clay can have lumps in it as long and they can be broken down during the mixing process. I use a standard five gallon plastic bucket. After filling the bucket about half full of slip, I mix the clay very well with a paint mixer attached to a standard drill. The best paint mixer I have was purchased for $6 at a Home Depot and is very heavy 3” spiral type mixer. This type of mixer has an enclosed mixing head with a spiral attachment on top that creates a very heavy vortex flow within the bucket. It is very important that the wet clay is well mixed and that all of the lumps are worked out of the clay prior to the addition of the paper fibers. Mix the clay until the mixture looks like thick yogurt or pancake batter. At this time, at your option, you can add a small amount of bleach (about one tablespoon) into the mixture to retard bacteria and reduce discoloration of the mixture. Adding bleach is not necessary when using cellulose insulation and may be omitted. Mix the clay and paper fibers together. The mixture will thicken or gel; this is a normal part of the process. Let the mixture set for a short time, and mix again. The final mixture should be very even in color and a smooth texture. At this point the mixture should be thick enough that you can remove the mixture from the bucket to a drying bat or rack with your hands. After drying to the desired consistency, the paperclay can be stored in airtight plastic buckets. If you use paper instead of cellulose, use the paperclay quickly, taking care not to make more than you can use in a week. Cellulose insulation based paperclay can be stored 3 to 5 weeks without spoilage. Store all paperclay in a cool, dark place. If mold does form on the surface of the clay, spray the surface of the clay with a spray bottle filled with water and a very small amount of bleach.
All types of paper can be used for paperclay. Many people use toilet paper because it is very fine milled paper and is easily broken down in the mixing process. There is a very good reason not to use this paper source. Toilet paper contains starch as a sizing material. When broken down in the clay mixture, toilet paper will begin the process of rotting almost immediately. Paperclay made from toilet paper will turn dark gray and start to stink in about ten days. The paperclay will work fine, and when it burns out in the kiln will return to the clay color without a change in the fired state. Don’t use paperclay that has begun to turn black. There could be a health hazard associated with the use of this material. I recommend that you use other kinds of paper which is less expensive such as newspaper pulp. Put the paper in hot water and after the paper has soaked up the water mix the paper with your paint mixer until a thin paper pulp is achieved. Strain the paper pulp from the water and add it to the clay mixture. It is very hard to break down this paper pulp. Repeated mixing is required to break out the individual paper fibers.
A better idea than the paper….
I recommend that you use another source as your paper fibers. Cellulose insulation is made from ground up newspapers and is available at most building suppliers and lumberyards. The advantage of this material is that it is comprised of ground up newspaper and chemicals to retard spoilage and fire. It doesn’t rot, turn black or smell when it is stored as wet clay. Cellulose is sold in 30 lb bags and costs about $6 per bag. One bag of insulation should be enough for almost any size studio. I recommend that you limit the amount of paper in clay (porcelain) to 5% or less by volume. Cellulose insulation is regulated by the government and Underwriters Laboratory, and has a lot of testing that it must comply with. Look for a rating of 515D (part of an identification number) on the bag. Almost all cellulose manufactured has this rating and should work well for paperclay. Cellulose is manufactured with boron and borax, which reduces the chance it will spoil when installed in an attic area. These two materials make cellulose a very good addition to clay. Cellulose when added to clay will not turn black or cause a bad odor. Cellulose, because of its very fine texture is easy to add to the clay slurry because it is already broken down into the fiber state and does not require any water bath or mixing prior to adding to the clay. Just add the dry fibers to the clay mixture and mix the clay well. For the amount of clay used in the five-gallon bucket, I use between 200-300 grams of cellulose. About 800 grams of paper to the five gallon container is about the limit. Above this amount could be used for large hand-built forms but not recommended for general hand building. This would amount to about one gallon of loose packed fibers taken from the bag of cellulose. Resist the impulse to put a lot of paper fibers into the clay. A small amount of fibers in relation to the amount of clay works well. Too much paper and the clay will have problems in the fired state. (I use porcelain; too much paper causes the clay to be very translucent, hard, glass like, and tends to dunt in the glaze firing.) When using red earthenware, or stoneware clay, you can use much more paper. Porcelain can’t take as much paper and will experiences excessive shrinking and warping, due to the borax, if you use more than the amount listed above.
After you have added the paper fibers, mix the clay with your paint mixer for several minutes. I would also recommend the addition of one to two tablespoons of bleach to the mixture. (Recently several people have been using Spic and Span which is a dry powder floor cleaning product to add to the paperclay mixture to retard spoilage. I’m not sure this is a good idea.) Make sure the mixture is even in color and all the material on the bottom of the bucket is well mixed into the paperclay. The mixture should be much ticker than when you started. It is a good idea to let this mixture set about fifteen minutes and then mix it again. The water in the clay will continue to soften the paper fiber and it will get ticker. Place this mixture on a drying bat to dry the material to a workable consistency.
Don’t store the wet (slurry) clay mixture for any length of time. It appears to me that the wetter the mixture, the more prone to rotting the mixture is. Storage of the paperclay is very important. Store the clay in an air tight container and put the container is a cool place. During the summer, sun or heat will cause the clay to rot very rapidly. Don’t store the clay in a clear container (I have made this mistake.) When working with the clay, allow all scrap materials to dry out. When you want to recycle clay, wet the clay with warm water at the last moment and mix it into the batch of new clay. Paper clay slip, used to bond joints when hand building, has a tendency to rot because it is stored in a wet slurry state. This wet slip will need the addition of bleach from time to time to prevent rotting.
Rotting Problems…. Store all paperclay in a cool, dark place. If mold does form on the surface of the clay, spray the surface of the clay with a spray bottle filled with water and a very small amount of bleach. Paper clay when stored in a warm place or for extended time will form mold on the inside of the clay. If this rot forms the clay should not be used. The paper clay can be used again by allowing the clay to dry and then putting the dry clay in water with a small amount of bleach in the water. Add this slurry mixture to your next batch of paper clay.
People have made the recommendation on Clayart and other internet locations that a way to prevent rotting of paper clay is to add Thymol to the clay. I do not recommend that you add this chemical to the clay. Thymol can be absorbed through the skin and is an irritant, especially to the eyes. Read the safety information about the chemical prior to any use at http://website.lineone.net/~dave.cushman/thymolsafety.html. Thymol is used by adding the crystals to rubbing alcohol. A very small amount of this alcohol (cap full) is then added to the clay mixture. Thymol has a very distinctive odor. Once added to the clay it can’t be removed. Thymol remains in dry clay that may be reprocessed and could contaminate future batches of your clay.
I dry my paperclay on bread racks that I got at a local store. These bread racks are about four inches high and 30’ square. They are made out of the same plastic that the five gallon bucket is made of and used to deliver bread to the local store without crushing the bread during delivery. They are made so that they stack on their corners without touching the bread. I spread a cloth mat on the bottom or the rack and spread a two-inch tick layer of the paperclay on top of it. I then stack the bread racks up and the clay can dry rapidly because of the airflow around the racks. This method of drying clay works very well for all types of clay and is a better way than using plaster bats. When the clay is dry to the consistency I like, I remove the cloth backing and store the clay in large plastic containers. Remember to store the clay in a dark cool place. Try not to use a clear storage container.
Properties of paperclay:
You can make paperclay out of any clay body that you are currently using.
Paperclay increased the dry strength of the body so that moving large pieces is less of a problem. Paper in the clay “opens” up the clay body so that you could work with much thicker walls for sculptural forms. Water vapor will escape the walls because of the paper; the threat of exploding walls is reduced.
When working on sculptural forms, you can add multi-layers of clay. These additions can be added at any point in the forming process. You can add wet-to-wet, wet-to-dry, or wet-to-bisque. (Yes, you can add wet clay to bisque and re-fire the piece.) Paperclay will withstand multiple re-dampening to make changes in the form. Paperclay will withstand forced drying. Paperclay allows for late stage additions to a piece. Even when dry, paperclay will stick to the form and allow changes. It is easy to cut a handle off a piece and reattach a better handle.
The fired results of paperclay are the same as regular clay. The piece will be lighter, and will shrink a little more that standard clay. Ash from the paper, and borax in the cellulose will act as a slight flux in the clay body. Use a cone 10 porcelain body and fire to cone 6 to correct for the flux problem. No change in formulation is necessary for stoneware or earthenware.
Short paper fibers are better than long fibers. Long fibers, or even other materials such as nylon or fiberglass do not add advantages to the clay. They are hard to cut and decrease workability. Don’t use glossy or color papers in paperclay. Ink used on newsprint will not add color to the fired clay.
Paperclay reduces the weight of the clay body because the paper replaces part of the clay with the lighter paper fibers.
Paperclay can be used on the wheel. But, a better ides is to use the regular clay on the wheel and use paperclay if you attach any handbuilt additions to the form. Handles made out of paperclay are less likely to crack and the paper helps bind them to the surface.
Paperclay slip is very good joining glue when handbuilding forms. The paper fibers in the clay increase the strength of the dry bond.
Paperclay can be used a repair material for cracked pots. (It’s usually better to discard a broken pot and spend your time making a better one!) The clay, along with paper slip can be forced into the crack for a repair. The paper helps to hold the patch in place and increased the bond of the repair.
Paper when added to clay in the amounts listed in this paper will not cause damage to an electric kiln. Increased amounts of cellulose, fired in a bisque kiln at a fast rate could cause a small amount of smoke in the kiln room. If this is a problem, reduce the amount of paper fiber in the clay, or fire the kiln at a slower rate for the first 1/3 of the firing. Adequate ventilation is important in all kiln firings. In most cases, the addition of pieces containing paper will not make any noticeable difference in the firing process.
Sources of cellulose insulation can be obtained through local insulation distributors. Look in your local phone directory yellow pagers under insulation. Call local insulation installers and ask to purchase a bag of insulation. Of the large building materials sellers in the Philadelphia area only Lows sells cellulose insulation. One bag of insulation will last you a very long time! (At the Clay Studio in Philadelphia, one bag of cellulose lasted over a year with several people using it.
If you have questions or comments please contact me at firstname.lastname@example.org
I would like to thank the Clay Studio in Philadelphia and Canada’s Banff Center for the Arts in Alberta for providing help and support. By supplying me with residencies these valuable artist organizations have given me the opportunity to develop this work. I would also like to thank Rosette Gault and Graham Hay for their pioneering work in paper clay.
Rosette Gault http://www.paperclayart.com/ (Books and information)
Graham Hay http://www.grahamhay.com.au/paperclay.html (Very good information)
Banff Center for the Arts http://www.banffcentre.ca/ (Great Place for a residency)
The Clay Studio, Philadelphia http://www.theclaystudio.org/ (The center of the Universe)