Porcelain

Reprinted from "INSULATORS - Crown Jewels of the Wire", October 1971, page 27

Here is some information on some interesting porcelain transpositions that might answer some questions that have come up from your readers. There will be approximately 30 different transposition shapes in the Universal Style Chart in my upcoming porcelain book.

The first two are "MACOMB" units. As are all six of the known MACOMB units, these are dry process units. Since they are of a shape impossible to make in one piece in a multipart press mold, they are made in two parts and then glaze-welded and fired as one piece.

The first one (2-3/4" x 4-1/2") in Type 1, and it is in the Frances Terrill collection. It was a horrible design. Both parts were separately threaded, there being no counter bore in the upper part to facilitate axial alignment of the two parts, and there being no attempt made to align the thread pitch (by rotation registry) of the two parts. Either of these faults makes it impossible to seat the unit properly on the transposition peg.

The second one (2-3/4" x 4-1/4") is Type 2, and for obvious reasons most probably succeeded the other one as a design improvement. Note that the above problems disappear when the threads are all formed in the bottom part. I have this specimen in my collection.

The other two units pictured are two of the three known different types of porcelain two-part transpositions. The third one, Pittsburg High Voltage #16, is somewhat similar to the #4 here so I didn't picture it for you.

The #4 here is unmarked, and is unidentified. The #3 unit is a Locke although never included in any Locke catalog from 1897 to date. It is marked with the patent date for one-part transposition (May 22, 1894), but this is no great surprise an Fred Locke randomly marked his various patent dates on all his designs from what I have seen. I have seen this May 22, 1894 date on a number of different Locke cable insulators, circa 1898 - 1903.

I have included this Locke unit in this writing, since there seems to be some question as to how it was made, and the term "sawed apart" keeps cropping up from your correspondents. Needless to say, they would be referring to sawing the unit before firing. Fired porcelain is obviously non-machine and can be worked only by grinding or diamond sawing. I believe collectors have been led astray by the saw-like marks they see on the firing surfaces of the two parts.

During firing, glazed surfaces cannot be allowed to come in contact the sagger, lest the units become firmly welded to the later. Kiln furniture (firing supports) have never been used, as far as I know, in the manufacture of pin type porcelains. One entire surface in left without glaze as a firing surface - either top rest, skirt rest, or petticoat rest.

In modern methods (past 40+ years), this firing rest has been obtained by using a paraphin resist on the firing surface, applied by dipping in hot paraphin preceding the glaze dip. But it hasn't always been done that way. None of the early pin types show evidence of this "paraphin resist" method. I do not know when this change in method occurred, but specimens seem to indicate it was between about 1910 and 1920.

Close examination of all the early units (1888 to about 1910) in very revealing. It appears as these units were glazed all over, and the glaze then removed from the firing surface by one of several methods - turning, carving, rasping, filing, sanding, etc. With practice, you can tell these from the ones made with the resist method. The glaze always comes to a sharp and abrupt termination at the carving or filing area.

This Locke transposition in my collection, and the others I have examined like it, show definite rasp marks on the firing surfaces, evenly spaced and matching the rasp teeth cutting profile. Study the firing rests of any of your early porcelains, either dry process or wet process, and you will see this evidence of rasping, carving or sanding off of the unwanted glaze before firing.

This was an earthshaking discovery to me, as I had assumed that glaze-resist methods had been in use for a very long time. Certainly this method of glazing the unit allover and then laboriously removing glaze for a firing rest has to be the hard way. I will endeavor to find out more about this - why, when, etc. Meantime, how about some help from some of the collectors who are familiar with the history of the ceramic arts?

Jack H. Tod