PROCEEDING OF THE

ANNUAL CONVENTION OF

THE AMERICAN INSTITUTE

OF ARCHITECTS, 1871

The Convention met pursuant to adjournment, and was called to order by the Chairman, Mr. Upjohn.

The Chairman:

“Mr. John H. Sturgis, of Boston, will read a paper on Terra-Cotta.”

Mr. Sturgis read the following paper:

TERRA-COTTA AND ITS USES

“That history repeats itself is shown by the revival of the use of Terra-Cotta. Four thousand years ago, baked, cooked or burnt earth—terra-cotta— was common enough in Egypt, and was the building material of that people. It was used by the Greeks, by the Romans, and by various European nations in the middle ages, and now in the Paris Exhibition, proofs are afforded in all parts of it, that modern Europe is largely reviving the use of terra-cotta;” so writes Mr. Cole in his report on class 65 of the Paris Exhibition of 1867. On the clay cylinders which were found at Nineveh, are impressed, in characters still sharp and clear as when they were first produced, the names and acts of rulers who flourished more than three thousand years ago; and we see in the Etruscan vases and Tazzae, not only the beautiful art, the refined taste and the poetic imagination of that mysterious race, but also the judgment with which they selected the most durable material in which to hand them down to future ages. Indeed, all nations whose early history is known, whether Egyptians, Greeks, Romans or Gauls, have left us samples of their works, and the fact that in this practically imperishable material, we have presented to us, more completely than in any other, the thoughts and works of artists from almost fabulous antiquity, in every age and in almost every civilized country, down to our present time; this fact I say, may well incite us to a careful study of the uses and advantages to be derived from the employment of terra-cotta in modern architecture. Those of us who are acquainted with the beautiful examples of terra-cotta in Italy, certainly would wish to see this material used, as far as practicable, in countries like our own, where so much brick building is in vogue. Donato Lazzari, better known as Bramante, who lived 1444-1514, shows, in his Ospedale Maggiore, the church of S. Maria delle Grazie, and in other churches, as well as in private buildings in Milan, that much can be done in this material; the cloisters of the Oertosa, near Pavia; the Foro dei Mereanti, and many palaces in Bologna,vhave been treated with equal success. Many interesting examples are to be found in Ferrara, Forli, Pisa, Sienna and even Venice and Rome, with their marble palaces and rich basilicas, did not disdain works in terra-cotta. Now let me give you some examples of its more modern use. The whole of the exterior of St. Paneras’ Church in London, is faced with Portland stone ashlar. The Carvatidse, which are copied from those of the Erechtheum at Athens, are of terra-cotta. They were formed in pieces and cemented together around pillars of cast iron, which in reality support the entablatures. These blocks do not seem to have contracted very severely in baking, and have been chiseled in places to conceal the joints. This is a serious mistake, as the outer surface of terra-cotta always becomes vitrified, and where cut away often exhibits weather stains, which would render it more liable in our climate to succumb to the effect of frost. A singular method of employing the material is exhibited in those portions of St. Pancras 5 Church where blocks larger than (at that time, 1820) could easily be burned in one piece were necessary, viz., the enriched portions which have either been inserted in short lengths into recesses and grooved in, or merely stuck with cement against large blocks of Portland stone. This may be seen in the west doors, of which the architraves are enriched with terra-cotta rosettes stuck against the stone, while the enriched cyma and the bead are let into grooves in the stone in lengths of about a foot, the stones themselves being from three to four feet in length. Although one is at first inclined to condemn this use of terra-cotta, it has many points in its favor, as the exposed parts of the stone are the portions most liable to decay, and by thus making them of a very indestructible. material, the general durability of the building is increased. All Souls 5 Church, in Langham Place, London, is ashlared in Bath stone; the capitals of the columns are of terra-cotta. Now in both these examples the terra-cotta has withstood the wear and tear of climate and the effect of London smoke and soot far better than have the stone. They were both built about fifty years since.

Sutton Palace, near Guilford, in Surrey, is a remarkable example of Tudor building of the most elaborate kind, the ornamental parts of which, including the mullions and transoms of the huge windows, are of red and white terra-cotta. This was built in 1530, and some blocks and specimens of the material have been presented by the present owner to the South Kensington Museum. They are in excellent condition. The coats of arms inserted in the walls of Hampton Court Palace, of terra-cotta, are of red color. It has been exposed to an English climate for three hundred and fifty years, as it is certainly of the same date as the building. It is attributed to Maestro Giorgio, who was in England at that time. The modeling of the head of the Caesars is bold and vigorous, and although the work has been exposed to the wind and rain for ten generations, and the brick, the stone and almost every material used in the construction of the palace, is more or less worn and decayed, this substance was, until within the last twenty-five years, untouched by the restorer. It is now painted, and some parts which were damaged have been added in cement. It has also been used for the gateway of King’s College and various works at Cambridge; the frieze, capitals, trophies, figures, fountains, &c., at Buckingham Palace; the frieze and capitals of St. Paul’s School; the colossal statue of Britannia, on the Town Hall, Liverpool; the pediment with the subject of the death of Nelson; statues, &c., at Greenwich Hospital; the vases on the terrace in front of Somerset House; the statue of Britannia, twelve feet high, and all the figures, &c., on the Nelson Monument, at Yarmouth, facing the sea, the stone of which is rapidly decaying; the statues, &c., at the Bank of England; the rich Gothic Screen of St. George’s Chapel, Windsor; the tiles on the footways of New Westminster Bridge; all the ornamental work for the new buildings lately erected and now erecting at South Kensington, and also the huge Albert Hall. When it was first proposed to use terra-cotta at South Kensington, it was submitted to various tests; among others, the underpinning and some of the lower members on two sides of an open court, were built, the one of Portland stone, the other of terra-cotta. After a time it was found that the stone had changed color and showed premonitory symptoms of disintegration, whereas the terra-cotta had as clean and perfect a face as when first put up. The Church at Lever Bridge, near Bolton-le-moors, in Lancashire, which was built in 1845, an elaborate structure in the decorated style and with a spire of open tracery, is executed entirely of terra-cotta made on the spot; the pews, which are low and open, with bench ends and poppy heads, are moulded in terra-cotta and painted. The Bauschule, by Schinkel, in Berlin, is a remarkable example of the modern adoption of terra-cotta. In it, moulded bricks and terra-cotta are used with great success. The Phoenix Fire Office of London showed their faith in terra-cotta, by having escutcheons made of it and building them into buildings which they insured, but finding it inconvenient to remove the slabs upon the cessation of an insurance, they gave up the practice ; but you may still see some about the streets of London. In the “Builder,” of February 21, 1851, is figured part of a terra-cotta front of a Romanesque Gothic character; it is on the Lungo l’Arno, at Pisa. Sir Charles Barry used terra-cotta for architectural purposes in 1856, and, in later years, Mr. Gilbert Scott, Sir Digby Wyatt, Mr. Charles Barry, in Dulwich College, Mr. Butterfield, at Rugby, and Mr. Waterhouse, in the Manchester Town Hall, have all used it freely and with good effect. For further examples, I would refer you to the publications of the various manufacturers.

What is terra-cotta? We all know that the words mean burned earth, or, as we now commonly call it, burned clay—the purer the clay, and the freer from extraneous matter, the better the terra-cotta. My friend, Mr, Redgrave, who has had charge of the building of the Albert; Hall, says, “The clay from which the best white terra-cotta is prepared, is that which is found alternating with shale in the coal regions. The clay, as it comes up from the coal-fire, is generally very stiff and solid, from the great pressure to which it is subjected. To prepare it for manufacture, it has to be broken up and ground, and for good work those portions are selected which are most free from shale and extraneous matter” Another authority says, “ The principal ingredients are white potter’s clay, fragments of the best stoneware pottery, ground to a powder, pulverized, flint and glass.” Mr. Blash- field uses the clays of Dorset, Cornwall, and Northamptonshire, Lynne sand, ground glass, pegmatite or china stone, feldspar and flint, also broken terra-cotta or burnt ware pulverized, and for very light porous articles, fossil bone is used with terra-cotta. In my judgment, all baked earths, no matter what the other ingredients, if properly burned, are terra-cottas. Terra-cotta should be sufficiently hard to resist the scratching of a pin, and if of a very superior quality, of an iron point. The variation in color in white, buff, and red terra-cotta is principally due to the clays, but in a measure to the amount of heat to which it has been subjected. Other colors, such as black, grey, green, blue, &c., are obtained by the mixture of mineral colors with the clays and other substances forming the body of the ware. These ingredients are well incorporated together by means of a pug-mill, and moistened to a consistency stiff enough for modelling or moulding into the shapes required. In the case of bassi-relievi, enriched pands, friezes, or sculpture, either of animals, flowers or figures, as the material actually built in is the same as that modelled, or, in other words, as the model itself is burned, they cannot be copied, and are and must remain the sole originals, and can, therefore, never occur except in the buildings for which they were specially designed. When the same form of design has to be often repeated, it is desirable, for economy’s sake, to make a model, and from this a mould. This mould is made of coarse plaster, and is from one and one-half to three inches in thickness. The clay is forced into the mould by hand, and thoroughly squeezed into all the crevices—the size of the object determining the thickness of the clay. Cell walls are left in the interior to support the clay in drying, as well as to increase the strength of the block: the thickness of the clay being reduced as nearly as possible to a uniform standard throughout to secure the equality of drying and firing of the material. The average thickness of the terra-cotta is from one to three inches, according to the size of the block. Some makers fill up their blocks, leaving only a few small holes to allow of evaporation; but the hollow blocks are preferable, as being more liable to dry and burn equally, and also for the facility of handling and the better bonding with the brickwork. The clay remains in the mould about twenty-four hours, by which time it has shrunk away from the piaster, and may be removed from the mould. The workman then finishes up the clay block, adding those parts which may be incomplete or damaged. It should now stand from ten days to a fortnight, according to the season, to dry. It is then placed in the kiln and burnt, with a steadily increasing heat, for five or six days, say till it reaches a heat at which soft iron will melt, after which the kiln is slowly cooled, and the finished blocks are taken out ready for use. Small inaccuracies may be remedied by rubbing-down the edges with a stone—no easy matter with good terra-cotta. The manufacturer must have accurate drawings of the works to be erected, with each block properly numbered, and he should be made, by contract, to supply no piece of ware which shall not properly fit with its neighbors. Great accuracy is required in the drawings (which must be made one-twelfth larger, to allow for shrinkage) for terra-cotta, as compared with those for stone; for, whereas an error in form or dimensions in the latter may be remedied in a day or two, it requires from eight to ten weeks to replace a piece of terra-cotta which may not come up to the mark. Plenty of time must, therefore, be allowed to the manufacturer. Now, in this country, where we are sometimes required to put up a building with the rapidity of a slave of the lamp, this is a serious drawback.

There is a difficulty in burning blocks -which are to constitute jambs, strings and continuous features, so as to be perfectly true and correct in the mouldings, but a marked improvement has taken place of late in this respect, and if the manufacturers would only pay sufficient attention to the essentials of drying, burning and cooling, even this difficulty may be obviated. The risks referred to are much reduced if the size of the blocks is not too great. For architectural work, the smaller the pieces, or the nearer they approach to the size of a large brick, the more economical will be the work. At the same time there is no practical objection to using terra-cotta in large pieces. These large hollow pieces which may have to carry heavy weights may be tilled at the building with fragments of terra-cotta and Roman cement, or with cement grouting, which must be mixed very poor; as the cement, especially Portland, if mixed too rich, very often expands so much in setting as to burst the terra-cotta all to pieces. Eight parts of sand to one of good cement is strong enough for the purpose.

I have lately received a photograph of Dulwich College—completed—in which the long lines of string courses, are as straight to all seeming as they could be made in any other material.

The blocks themselves may be carefully bonded in with the brickwork in cement in proportions of three of sand to one of cement, the face joints being raked out and pointed with a mixture of one part of terra-cotta to one part of lime. There are some, of course, who depreciate this valuable and efficient material; stating that it is unlit for exterior use, and that it is very expensive. Now, this is quite a mistake, for it is much less expensive than stone and more durable than almost any building stone when the proper materials are used in mixing and when it has been well burned; for the high degree of heat to which it is subjected causes it to become a semi-vitrified substance and renders it quite impervious to the weather. Frost or damp has no effect upon it; consequently it retains a sharpness and surface unimpaired by atmospheric changes. The fragments of terra-cotta in the British Museum fully bear out this remark. Almost a century has elapsed since the introduction of terra-cotta into England, and many works done in it may now be seen in as perfect a state as when first executed; while the stone-work in the same building will in many instances be found to have gone to decay. It is in London almost the only material which is able to resist the action of the weather and the acid gases contained in the atmosphere.

THE STRENGTH OF TERRA-COTTA AS COMPARED WITH STONES IN ORDINARY USE

I have here a table of experiments upon terra- cotta, manufactured by Mr. Blashfield, of Stamford, and carried out at the testing works of Mr. Kirkaldy, at Southwark, showing the results of 46 experiments made with different-shaped pieces of terra-cotta, some of them solid, some hollow, but left empty, and some with the hollow blocks filled in with brick and Roman cement. The result of these experiments shows that the filling-in doubled the strength of the hollow blocks, as the one showed signs of cracking, with a strain of 42 tons to the square foot, and the other required 86 tons to produce the effect. In these experiments the ware was only 1-J in. thick. A solid 12 in. cube of terra-cotta did not show a crack till a strain of 442 tons was put upon it, and to crush a hexagon stable floor brick 4 in. in diameter and 2-J in. thick, required no less than 855 tons. The red terra-cotta which was used for the shafts to jambs, and mullions of the principal floor windows of Dulwich College were proved to be capable of bearing a pressure of 246 tons to the square foot. In experiments to test the wearing capabilities of terra-cotta tiles for foot traffic on Westminster Bridge, the friction of sharp sand andw r ater was applied to a terra-cotta tile 12 in. square, and a piece of York stone, somewhat like in appearance and substance our North River stone—for five hours, at the end of which time it was found that the terra-cotta tile had lost 1/16 in. in thickness, and the York stone had lost 1/4 in. Of course all these tests apply only to such terra-cotta as has been properly mixed and thoroughly burned.

Besides the advantage of durablity and strength, the use of terra-cotta at times effects a saving in time and, consequently, in expense. It has been estimated that had the bas-relief of the pediment of Greenwieh Hospital been executed in marble, it would have required somewhere about ten years to have completed it, but in terra-cotta it was done in two years.

There comes in also the practical question of weight and, consequently, the cost of transport, for with terra-cotta, unlike stone, no unnecessary or dead weight has to be carried, for it must of necessity be modelled of its proper size, and moreover, as for thoroughness of burning it is made of moderate thickness and hollow, the weight to be conveyed is reduced to a minimum.

Granite (Quincy) weighs 167.75 lbs. per cubic foot. Sandstones generally from 103 to 167 lbs. Ohio or Buenavista stone, 144 lbs. Solid terra-cotta weighs 122 lbs., and a hollow cube 2 inches thick, weighs but 68 lbs.

Mr. Barry writes, “ On the subject of the cost of terra-cotta work, I will mention some facts, by way of examples, which, as far as they go, are highly satisfactory, but the cost of terra-cotta must be largely reduced as it becomes more extensively used, for in this case, no doubt a reduction might take place in all the items of the manufacture. Still, with all the existing drawbacks, the economy of terra-cotta as compared with stone is great. Speaking in general terms, it may be said," that taking cube for cube as fixed in a building, terra-cotta costs a little less than soft stones, as Bath, &c,, while as regards Portland, the average differences would be about 35@40 per cent. The greatest economy is to be found when there is much work either in under cutting of mouldings, which costs nothing extra in terra-cotta over ordinary mouldings and in artistic modelled work.” Mr. Barry further states that (( The ground floor windows at Dulwich College were made and fixed complete for £19 each; their cost in Bath stone would have been £20, and in Portland £28. The principal floor windows, which are of rather elaborate design, were fixed complete for £41 each; they would cost in Bath stone £57, and in Portland £86. This cost includes the modelling the busts in high relief.

These windows did not come, with all their work, to more than 5s. 6cl per cubic foot. The second floor windows have been fixed complete for £10 each; m Bath stone £19, and in Portland £28 10s. each. The cost of the cornice, which is 15 in projection and 4 feet high, exclusive of the stone corona, fixed complete, is £1 13s. per foot run; m Bath stone it could not have been done for less than £4, and in Portland £6 per foot run. Hollow blocks of an average thickness of 2 m. and filled in with broken terra-cotta or brick in Roman cement, the cost may be stated as 3s. Id. per cubic foot. The relative cost, taken in the same way, would be 5s. 6d. for Bath stone, and 9s. for Portland.”

In the South Kensington Museum is an ornamental mullion carved in stone and the same work executed in terra-cotta. The relative prices were put down very accurately, and were as follows: £5 8s. for the work in Portland stone, and £2 3s. for the same in terra-cotta. How in this country, where skilled labor is so much more costly than in Europe, I place the comparative difference in the cost of terra-cotta and stone for elaborately carved work at 80 to 90 per cent., and for plain ashlar at from 25 to 30 percent, in favor of the terra-cotta in point of cheapness.

Mr. Sims offered a resolution of thanks to Mr. Sturgis for his able and interesting paper.

A protracted discussion on the advantages and disadvantages of the use of terra-cotta, between Messrs. Sims, McArthur, Stone, Sturgis, Richard Upjohn, Fernbach, Ware, Wight, Hatfield, and others, then followed.

The Convention adjourned until two o’clock.

ABOUT JOHN STURGIS

Born in 1834 in Macau, China, John Sturgis was the son of a wealthy Boston merchant active in the opium trade. He attended Boston Latin School and then lived abroad in London where he studied architecture under the tutelage of James Colling. In 1861, Sturgis returned to Boston with his wife, Frances Anne Codman, where he found work at Bryant and Gilman before opening his own practice, Sturgis & Brigham, in 1866. Sturgis was known for his work in terra-cotta from his days in England through his time in Boston. While some of his terra-cotta work still exists, including the Codman Building at 10 Liberty Square, and the Ames-Webster Mansion at 306 Dartmouth Street, much of his more prominent work, including the Isabella Stewart Gardner House in Beacon Hill and the original Boston Museum of Fine Arts, are no longer standing.