NOTES ON FIRING TERRA COTTA1

Some notes are given on the firing behavior of a 14-foot diameter muffle type terra cotta kiln, using coal as a fuel. The need of more data on periodic fired kilns in all branches of the ceramic field is stressed.     

BETTER TERRA COTTA SLABS1

Terra cotta slab problems are discussed as to (1) refractoriness, (2) mechanical strength, (3) accurate dimensions, (4) temperature changes, (5) spalling, (6) thermal conductivity, and (7) abrasion. Mixes of two experimental bodies are given. The second consisting of 30 grog, 15 clay of low plasticity and 55 bond clays gave satisfactory results.     

TERRA COTTA KILN SLAB INVESTIGATION1

Following several discussions as to the constitution of a good kiln slab for terra cotta manufacture, a coöperative test was made in which slabs of various compositions were manufactured by a producer of refractories, tested under actual service conditions, and physical measurements were determined by the Ceramic Department, Rutgers University. Series included the use of tight-firing medium refractory clays, open-firing refractory clays with grog, both vitreous and porous. Grogs were sized (definite proportions of size ranges constituting the different members). Conclusions were drawn as to effect of all these variables.     

TERRA COTTA IN ARCHITECTURAL DESIGN1

Emphasis is made of the use of terra cotta as an artistic and decorative material. Its successful use demands an architecturally educated talent and a ceramic chemist who appreciates texture, hue and the required colors. The tendency to employ terra cotta to bring out effects of stone masonry design is shown.     

SOME FUNDAMENTALS OF TERRA COTTA1

Terra cotta is not a definite material. Considerable difference of opinion exists as to suitable structure and composition. There are more differences between different makes of terra cotta than there are in opinion as to what it should be. Microscope study of thin sections of terra cotta is a valuable method of examination. The voids in terra cotta are of more than one kind and origin. The grog used in terra cotta is frequently unsuitable as to character and size. A fuller knowledge of fundamentals will probably much alter ideas as to suitable grog. A test for internal stress is described. Terra cotta was tested for osmotic action. The internal degradation of terra cotta is demonstrated by two different methods. A number of slides are presented being typical of certain characteristics.     

FIRING CERAMIC WARE WITH GAS1

The significance of the terms oxidizing and reducing kiln atmospheres to the ceramists and the gas engineer is discussed. The applications, advantages, and comparative costs of various fuels used in the ceramic field are considered.     

NOTES ON SHIVERING OF TERRA COTTA1

Six terra cotta clays are tested for shivering as a body trouble using a white mat glaze, at cone 3 starting. One non-shivering clay and one badly shivering clay are experimented with, to produce and overcome shivering. Causes of Shivering .—From this work and that of others which has been checked, uses are

• 1 presence of finely divided silica in the body, from

• (a) highly siliceous clays
• (b) finely ground grog of a siliceous nature

• 2 presence of soluble salts in the clay, grog, or tempering water
• 3 longer firing periods

Methods of Eliminating Shivering.

• 1 Use of a flux such as feldspar, felsite, or similar rock to overcome action of fine silica
• 2 Use of coarse grog or sand
• 3 Use of barium carbonate to overcame effects of salts

     

NOTES ON TERRA COTTA GLAZE CONSISTENCY1

Some of the difficulties encountered in applying glaze to terra cotta are discussed. The use of a hydrometer to test glazes is misleading as a hydrometer supplies gravity indication only in true solutions and glazes are not true solutions; furthermore the viscosity of a glaze may obscure the real specific gravity. It is suggested that in order to Control a glaze it should first be made to a desirable specific gravity and then the desired viscosity at that gravity be ascertained by experiment. A viscosimeter and specific gravity bottle are suggested for this purpose. The effect of change of alkalinity and of bacteria together with the control of glaze wastage are also discussed.     

SOME EXPERIMENTS ON TERRA COTTA SLIPS1

A series of experiments on slips for terra cotta, in which variations in composition in relation to their effect on vitrification, crazing, cracking, and color are studied.     

SOME OBSERVATIONS ON TERRA COTTA PHYSICS1

An apparatus for determining a representative “over-all” coefficient of thermal expansion of terra cotta under service conditions is described. Observations made show a decided contraction upon wetting the terra cotta and the temperature must be raised for the regaining of the original length. It is probable that the extent of mycelial capillaries is the determining factor of the magnitude of contraction. Further data obtained are presented and discussed.     

A TERRA COTTA INDUSTRY FOR OHIO1

Two terra cotta industries using Ohio clays existed in Ohio prior to 1860. Today no terra cotta industries exist within the State, although Ohio has the clay, fuel and skilled labor. One Ohio clay, the Tionesta or No. 3 B, is especially adapted for terra cotta. It crosses the state through Vinton, Hocking, Perry, Muskingum, Coshocton, Tuscrawas and Stark Counties. The occurrences and chemical composition as determined by the Ohio Geol. Survey are given by the author. This clay burns with a shrinkage of about 6 per cent and a porosity of about 8 per cent from cone 2 to cone 5 with practically no color variation. It will carry its own weight of non-plastic without serious loss of mechanical strength. Successful combinations and working directions for body, engobe, glaze and vitreous slip are given.