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and apparently "just because."

Plate XXII. Fig 6. — 300 Diameters — Slide from an insulator that after passing factory test was stored in a warehouse two years
Failed under flash-over voltage when taken out — The crack A is apparently due to expansion and contraction and is not a cooling crack as no crystals have formed in it — The cement in this insulator was very porous and showed the effects of expansion and contraction — Note the flow structure crossing the picture between the large quartz crystals and the alignment of sillimanite along this flow.

Plate XXII. Fig. 7 — 300 Diameters — Same as Fig. 6. under crossed nicols
Note the great amount of fine quartz crystals and their concentration due apparently to flow in the mass before or during firing.

ex W. D. Peaslee. "The Insulator Situation." Transactions of the American Institute of Electrical Engineers 36 (1917): 527-533

In other words, they deteriorate at an alarming rate even doing nothing and apparently just 'because'.From a study of the insulator troubles of several systems for the past three years, and from a microscopical analysis (using polarized light and crossed nicols) of several hundred insulators whose records were known, the following points regarding the deterioration of the porcelain insulator...

a form of haruspicy in the (industrial) middens, great pile of failure (like these), failure upon failure.

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tags: W. D. Peaslee; just because; the insulator situation; haruspicy; failure