Glazing Notes On Guy Strain Insulators

Reprinted from "INSULATORS - Crown Jewels of the Wire", October 1972, page 28

The following information is extracted from answers I have written to several readers in the past, and I trust it will answer the same question for others as well.

Guy strain insulators are many times used near the ground at eye level or on horizontal guys where a large white area (unglazed firing surface) is rather unsightly and also given a quick impression of a damaged insulator to passing line crews. Porcelain companies have worked out several methods of producing guy strains which don't have this objection, and some methods are described here. Taken in a general way, this will also explain any other similar versions you may happen to encounter.

The first method is to simply minimize the unglazed white area by using small, circular firing rests or by using three or four small firing teats. Since this does not involve extra manufacturing steps and yet given fairly satisfactory results, it is now used by most companies.

A method used by all the major companies at one time or another was to glaze the insulators overall and then fire them on a layer of porcelain "sand". The insulators were broken out after firing and had the objection of some rather sharp particles on their ends - not to mention an even unsightlier appearance on some versions.

Franklin Porcelain (& possibly others) left the usual unglazed area on the end but then painted this with an altered glaze slip low in fluxing ingredients. These were fired on sand also, but very little of the sand stuck to the special glaze on the end of the insulator.

The best results seem to derive from the method used by Pinco. One end of the insulator is first dipped into a body slip which will fire dark. Then a paraffin resist is added to this end in normal fashion (but covering only the end of the dark body slip coating). The unit is then glazed overall and fired in normal fashion. This results in the insulator having a dark, unglazed end but without objectionable sand particles adhering to it. If I had to vote on the various methods, I would call Pinco the winner.