Dremel 876 Specifications download pdf (Page 8)

Many kiln operators feel that opening the kiln after the

firing is more exciting than Christmas morning. However,

firing is as big of a responsibility as it is a pleasure. It is the

most essential step the ceramist has in producing the

finished “objets d'art.”

Successful kiln firing requires knowledge and under-

standing of the equipment, what happens in the kiln during

firing, and the various reactions of the different items and

materials placed into the kiln. Learning these necessary funda-

mentals are easily obtained with reading and first hand

experience of the kiln. First of all, read and understand the kiln

manual. If you do not have one, write to the manufacturer and

they will send the materials needed to operate your kiln.

There are several types of kilns available. Basically,

kilns are specially designed ovens used for firing (baking)

ceramic objects to a very high temperature. This oven

converts the raw materials into ceramics by subjecting them

to high temperatures. While the electric kiln is most

commonly used kiln, there are also other types of kilns

fueled by oil and gas. The gas and oil are the least

practical, due to their fuel source and their interaction with

the types of glazes used with whiteware.

Kiln installation should be done by a qualified

electrician. Check with your electric company for peak

power demands that can affect your firing. If fuses or

circuit breakers trip during firing, lower amounts of voltage

will go to the kiln, causing the kiln to perform incorrectly.

The location of the kiln should:

•Be on level concrete flooring or an asbestos pad.

•Be located in a well vented room.

•Be located in a protected area, away from foot traffic.

•Allow easy access to the kiln opening, controls and

peepholes.

•Be near the correct electrical outlet. Check the

manufacturer’s requirements for voltage needs.

•Do not allow the pigtail cord or power supply cable to

rest on the side of the kiln.

Pyrometric Cones

The kiln operates using degrees of heat more

commonly referred to as cone numbers. There are several

types of cones and numbering systems for ceramics

throughout the world. The one most accepted in ceramics

is the Orton cone, determined at the National Bureau of

Standards. There are other types and standards that may be

applicable in countries other than the United States.

The pyrometric cone is a small elongated triangular

pyramid composed of clay and other materials. These

cones are a self deforming ceramic piece, that when

subjected to heat and time, signal the kiln sitter (see below

about kiln sitter) that the kiln has done the necessary work.

When the cone has deformed to its specifications, the

objects in the kiln have reached the equivalent of the

needed temperature and length of time to mature the

products used.

Cones are a necessary, vital tool in ceramics, signaling

the user that time and temperature have been obtained.

While an extremely slow firing or fast firing can fool the

cone into deforming at a different temperature, cones are

still a very important part to the success you have creating

beautiful pieces.

Fast Firings

Fast firings or rapidly increased temperatures should be

avoided. The rate of temperature should be approximately

250˚ to 350˚ per hour. The temperature rate should never

exceed 500˚ per hour. Most automatic kilns are in the 350˚ to

400˚ rate per hour range. This is important factor for you to

know. Too fast of a firing will not allow the piece or the

glazes to mature. The result will be lackluster color, chalky

surface or immature bisque that can cause problems later in

firing. Although a cupcake can be cooked within minutes of

putting it into the oven, a fruitcake will take several times that

to fully cook; a hotter oven would simply burn the outside

and leave the inside uncooked. The same applies to

ceramics.

Types of Cones

There are two types of cones: small cones (1

⁄8

inch) are

used in the Dawson Kiln Sitter (see page 8 for explanation of

kiln sitters) that allow the kiln to shut off when the ware has

matured. This can be a triangular pyramid or a bar. The large

cones (2

⁄2 inch) are called shelf or witness cones. These two

types of cones are not interchangeable in their usage; each

has special needs in order for them to perform as designed.

Shelf or Witness Cones

The large cone commonly referred to as the shelf cone

(or witness cone) is the back-up system to the kiln sitter.

These cones are placed throughout the kiln during firing to

show what is happening during your firings.

Check the cones when they are broken apart from one

another. If there is a hollow spine on the cone, do not use

it; the cone will deform incorrectly during the firing, giving

you a misreading. Shelf cones can be self-supporting or

held in place with some form of holder, as long as they are

at an 8 degree angle. The self-supporting cones eliminate

any error of a wrong angle. Ideally cones should be placed

in the middle of the kiln shelves with a clear visual path to

the peepholes and to the element behind the cone for ease

of viewing during the yellow-hot temperatures. Even if the

ideal is not obtainable, shelf cones should be placed

throughout the kiln on shelves out of a draft and three

inches from the kiln elements.

Shelf cones are used in a series of three:

• The Guide Cone is one cone cooler than the desired

firing temperature.

• The Firing Cone is the cone temperature you wish to

achieve.

•TheGuard Cone is one cone hotter than the desired cone.

All Fired Up . . .

Kiln Firing and Operation

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Dremel 876 Specifications Page 8

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