Mica

in Pressure Lamps like Petromax, Aida, Hasag etc.

DEUTSCH

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In the early days of pressure lamps the cylinders, or globes, were frequently not made of glass as the glass manufacturing technology of the time would not permit production of a glass cylinder combining the requirements of thickness, heat resistance and low price. So mica(or isinglass) was used as a simple cheap alternative.

Mica is a very good electrical insulator and has very good heat conducting properties. It has been used in the electronics industry for years as insulation for power transistors Etc.

In pressure lamps mica suits very well as a material for making globes / cylinders. When cut into strips and assembled correctly it offers a variety of design possibilities for globe manufacture.
Because it is also to a degree flexible such a mica globe can even be dropped without breaking, is resistant to most chemicals but it is easily damaged by scratches.

Original Mica Globe of the 1940s.	Reproduction Globe by Fred, 2004.
A brand new pane of mica 5x5" x 1/128" thin.
Different sizes of mica sheets are available at Stuga-Cabaña / Glimmerscheiben Mica.
To demonstrate the performance of mica when subjected to a variety of chemical, temperature and mechanical trauma, I cut this sheet into pieces and maltreated it in different ways.
I cut the mica in such pieces.	...and did this to the edges!

Essence of Vinegar 25% (pure)	Toilet Cleaner (cheap)	Dishwasher (Miele)	Caustic Soda (extreme)	Bunsen Flame (hot)	Nail (pointed)	Axe (brutal)


24h later	24h later	4 cycles later	24h later	some seconds later	3 scratches later	3 cuts later


Result: Superficially no damage, no visible changes. Vinegar laterally penetrated the laminations between the single sheets of the mica.	Result: Superficially no damage, no visible changes. The toilet cleaner laterally penetrated the laminations between the single sheets of the mica.	Result: Superficially no damage, no visible changes. Dishwasher detergent laterally deeply penetrated the laminations between the single sheets of the mica.	Result: Superficially no damage, no visible changes. The caustic soda laterally penetrated a little between the single sheets of the mica.	Result: Complete destruction The heat of the Bunsen flame caused black-brown discoloration and a scale-like swelling.	Result: Deep scratches As expected.	Result: Complete destruction As expected. Cut into shreds, the single sheets of the mica went dull-grey.
In conclusion most liquids will penetrate the laminations of a mica sheet but the material is resistant to most chemicals. It is less good with physical trauma because scratching will separate the laminations and the material can start to break up which turns it partially opaque. However a direct impact, whilst possibly making a hole, will not destroy the whole globe as would be the case with glass. Mica also has the advantage of being lighter than glass and for a lantern designed to be carried this may be desirable.
I do not accept any responsibility neither for the correctness nor for the reproducibility of these results. I got these results. Other chemicals, temperatures or other qualities of mica will certainly cause other results!

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