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Woodfiring with potters for peace: Peter Chartrand details the work of the organisation with kilns for water filters.

POTTERS FOR PEACE (PFP) IS A US-based non-profit organisation working in the developing world with two programs. We offer training and facility set-up for the production of ceramic water filters around the world and in Central America we assist artisan potters with design, technical and marketing problems. These potters are primarily small groups of women in rural communities producing slip decorated earthenware woodfired from about 650[degrees] to 900[degrees]C. Often the first step in our work with potters is to improve firing. The goals for these woodfirers may differ significantly from what is in vogue for 'first world' artist woodfirers; low maximum temperature, clean atmosphere with no fire marks on the ware and a firing time that does not go much longer than one workday (eight to 10 hours).


These potters may use variations of a Mediterranean updraft kiln which can be quite satisfactory and, in some cases, (such as San Juan de Oriente, Nicaragua) produces highly refined ware. Others may be bonfiring or even, as in the case of two sisters in the mountains of northern Nicaragua, 'roasting' their pots in the same little fire used for food preparation, turning the pieces occasionally with sticks for an 'even' firing. PFP built a simple barrel kiln with the sisters and the quality and quantity of their output improved markedly.

In the mid-1990s one of PFP's then consultants, retired Professor Manny Hernandez of Northern Illinois University, developed a fuel efficient, downdraft wood kiln for one of the first filter production shops in Cuba. It typically has about a cubic metre capacity and is made with local red brick of the 'fired abobe' variety. Originally designed with a flat roof, now as often as not it is built with an arch. Two parallel fireboxes pass along the sides under the floor and enter the chamber on each side of the chimney. Heat exits at the front centre of the chamber into a trench leading back to the chimney.

In 1998, Hurricane Mitch tore through Central America and destroyed many kilns; Hernandez trained a Nicaraguan crew and in two months they built eight kilns. A grateful potter dubbed it the "Mani Kiln" and the name stuck.

PFP has tried various methods of sharing knowledge (including constructing a residential training centre and hiring a travelling design consultant) but often the best option is facilitating potters to learn from each other by encouraging and arranging visits and interchanges between pottery communities. For instance, visiting a more successful group is a way to see firsthand the advantages to improved firing and to initiate a request for assistance in building a Mani kiln or a new updraft kiln. Among the artisan potters of Nicaragua there is no movement in the direction of glazed ware. Much of the production, including time honoured functional forms, is now decorative, even for the in-country market. The goals are not necessarily higher temperatures but more to achieve an even firing, efficient fuel use and less breakage in the firing. The Mani kiln can supply these improvements along with providing enlarged capacity.

The technology package for production of the Potters for Peace ceramic water filter is based on the use of several machines; hammermill, mixer, hydraulic press and the Mani kiln. The PFP ceramic filter is based on a filter developed in Guatemala in the 1980s by industrial engineer Fernando Mazariegos; a simple pressed bucket shape of about 10 litre capacity made with a mix of about five-to-one by weight of milled and screened local clay and a burnout material; sawdust or rice husk, to produce the necessary porosity. The filters are capable of removing 99.9 percent of bacteria and other contaminating substances from water when properly made.



Potters for Peace does not own or operate filter production facilities. We work with a local partner/owner to transfer the technology. A PFP technical consultant typically spends one month at the start-up, training and working with the staff to arrive at a saleable filter using local materials. That usually involves building and firing a Mani kiln with two loads of test filters. Our preference is to train local potters as the workforce but, more often, young semiskilled workers from the community are chosen by the partner for the production jobs.

Firing filters with wood is challenging; they require an oxygen rich atmosphere to rid filters of all carbon; no more than one cone temperature differential in the kiln and completion of the firing in a 10 hour work day. To achieve the desired filtration rate of 1.5-2.5 litres per hour, the filters are fired to between 850[degrees] and 900[degrees]C (Orton cone 012) a temperature at which many natural earthenware clays are at the edge of usability. The potter/filter workers who may have previously fired their pots with grass bonfires or other rudimentary kilns now must manage a downdraft kiln, monitored with a multi-entry pyrometer and pyrometric cones.

In addition to the usual danger points at 100[degrees] and 560[degrees]C filter makers must carefully pass them through a combustible burnout phase at 350[degrees]-450[degrees]C. At this time the filters are being heated both externally and internally and a minimum of two hours is needed to go through this phase safely. Despite the fact that this takes place somewhat early in the firing, slowing the kiln can be a problem; the burning sawdust in a load of filters can produce more heat than normal stoking. Even the best kilns need tweaking and the Mani is no exception. The basic Mani kiln design tends to fire with the top of the kiln about 100[degrees]C hotter than the bottom and we have developed strategies to deal with this.

The chamber entries from the Mani kiln fireboxes are at the inner ends of the trenches and the fireboxes are covered with loose brick allowing gaps to be opened to provide direct vertical passage of heat and flames into the ware chamber. At the recommendation of UK potter Mike Finch, we recently added double doors to the firebox stoking entries. The door divides at grate level and closing the top door forces all primary air to enter through the ash area, slowing down the flow of heat and flame into the chamber and allowing the stoker to place the burning fuel anywhere from front to back along the grate bars. By placing fires closer to the stoking end of the firebox the temperature almost immediately rises at the bottom of the kiln and decreases at the top. Removing a cover brick from the firebox allows larger gaps into the chamber and the temperature can be bounced back and forth between the top and bottom and held even by moving the fires on the grates. The downside of this practice is that some of the filters on the floor level will be marked and possibly damaged by direct flame contact.



Another technique to even temperatures does not depend upon removing firebox cover bricks but utilises longer intervals between stokes and the heat passing through the smaller gaps. This stoking method must be carried out between 700[degrees] and 860[degrees]C. The fires are moved near the outside entrances of the fireboxes and, after stoking, the pyrometer is watched closely. The stoker will need to resist her instinct to stoke when the kiln's upper area temperature falls. After a stoke, it will rise strongly and, when it starts to fall, the bottom temperature will rise. Then when the latter stops rising, it is time to stoke again. The bottom will not fall off significantly and, using this stoking, the temperature of the bottom can be brought up incrementally. After firing, the filters are treated with colloidal silver. It is the combination of porosity and the silver that makes the filters effective.


Potters for Peace offers assistance to our fellow craftspeople in the developing world, with the goal of bettering their livelihoods. This is done in the belief that international peace and justice can be fostered through respectful friendships and equity in economic relationships. Today their membership consists of approximately 800 people, mostly potters, who help to fund their operations through individual donations and by donating their work to annual regional benefit sales. They have an active board of about 10 people, including a Filter Committee and four technical consultants who carry out their filter program. They continue to work with artisan potters to improve their equipment, their skills and their marketing opportunities.

A challenge for PFP consultants during the training is translating our years of firing knowledge into a usable protocol for filter shop employees. We try to establish long term relationships with partners to facilitate exchanges of information and possible return visits for technology tune-up. A common scenario in these filter projects is similar to the parlour game where a word is whispered in someone's ear and becomes unrecognizable by the time it has been passed through all of the players. Changes in staff and materials can have the same effect on filter production techniques.

Peter Chartrand is the US Director for Potters for Peace. He maintains a studio in Bisbee, Arizona, US.
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Author:Chartrand, Peter
Publication:Ceramics Technical
Date:Nov 1, 2011
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