Bologna bottle

A Bologna bottle, often used in physics demonstrations and magic tricks, is a glass bottle which has great external strength,

The exterior is generally strong enough that one could pound a nail into a block of wood using the bottle as a hammer, however even a small scratch on the interior would cause it to crumble.

It is created by heating a glass bottle then slowly cooling the outside whilst rapidly cooling the inside. This causes the external strength and internal stress such that even a scratch on the inside is sufficient to shatter the bottle.

The effect is utilized in several magic effects, including the "Devil's Flask".


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More information about the creation of Bologna bottles, and Bologna vials as they were more commonly known.

After learning that Bologna bottles were more commonly called Bologna vials, a little more information came to light.

It must be stressed that the creation process written in the section above is referring to Bologna vials only, as no definition could be found of a Bologna bottle at all. The definitions of Bologna vials varied however, some being of inner fortitude, some of outer, but neither author or definer seemingly aware in any way of the knowledge of each other's work. Although a definition of Bologna vials was in the 1913 copy of Merriam-Websters dictionary, searching today yields little else but sausage. As for "Bologna bottle", that appears to be a rather modern phrase for a flask shaped bottle rapidly cooled on the outside and slow cooled on the inside during the glass-making process. This causes the stresses to be concentrated on the inside of the flask, while the quick cooled, compressed, extremely hard, and otherwise incredibly brittle glass on the outside is held together by those powerful internal stresses. One teachers manual for the instruction on the demonstration and explanation of the Bologna bottle listed the manufacturing process as quick cooling a glass right after being blown, then annealing it from the outside again and as annealing specifies, allowing it to cool down slowly once more.

Definitions and related excerpts from the 19th and 20th centuries

excerpt from pg.124 of "A cyclopaedia of six thousand practical receipts, and collateral information in the arts manufactures, and trades including medicine, pharmacy, and domestic economy:... " by Arnold James Cooley pub. 1854

"BOLOGNA VIAL. The bologna, or philosophical vial, is a small vessel of glass which has been suddenly cooled, open at the upper end, and rounded at the bottom. It is made so thick at the bottom that it will bear a smart blow against a hard body without breaking; but if a little pebble, or piece of flint, is let fall into it, it immediately cracks, and the bottom falls into pieces; but unless the pebble or flint is large and angular enough to scratch the surface of the glass, it will not break."[1]

excerpt from pg. 450 of "The new American cyclopædia, ed. by G. Ripley and C.A. Dana" by American Cyclopaedia pub. 1859

"BOLOGNA VIAL, a name given to rudely shaped flasks of glass, which, in making, are suddenly cooled without annealing. They are made to illustrate the peculiar effects of the annealing process."[2]

excerpt from pg.110 of "Knight's American mechanical dictionary: ..." by Edward Henry Knight pub. 1876

"The Bologna vial is a rude flask of some three or four inches in length by about one in diameter, and from 1/16 to 1/8 of an inch in thickness.

If a leaden bullet lie dropped into it from a height of three or four feet, or it be struck a smart blow on the outside with a stick, it will not break, but the dropping of a grain of sand or a small sharp fragment of flint into it will cause it to crack and fall to pieces."[3]

excerpt from pg.158 of "The Locomotive, Volume 6", by Hartford Steam Boiler Inspection and Insurance Company pub. 1885

"The Bologna vial is simply a vial of any form whatever, made of any kind of glass, but much thicker at bottom than at top, and cooled immediately without annealing." ... "These glasses when they have received the first injury do not always crack immediately, but remain whole sometimes a few minutes, sometimes for hours, and then suddenly give way." ... "The peculiar brittleness of the Bologna vial is also removed by again heating and cooling slowly."[4]

The gentleman who wrote these lines was under the impression it was the "stoutness" of the bottom of the glass that gave it such resilience, and seemed unaware from his definition that the inside or outside of the glass being quench cooled had any bearing on it.

Websters Dictionary 1913

"{Bologna vial}, a vial of unannealed glass which will fly into pieces when its surface is scratched by a hard body, as by dropping into it a fragment of flint; whereas a bullet may be dropped into it without injury."[5]

excerpt from the Physics Department website on "Bologna Bottles" at the Univ. of Illinois at Urbana-Champaign 1996

"The Bologna Bottle has been heated and then the outside has been slowly cooled, rendering it hard enough to drive a nail into wood. The bottle's inside surface, however, has been rapidly cooled, maximizing internal stress. A mineral is used to scratch the inside surface of the bottle, at which, due to the internal stress, the entire bottle shatters."[6]

Know anything more? We sure don't!

Perhaps there are some financial impediments to the free exchange of knowledge on this subject. One is a magical effect based on the principle sold for $1000 a pop, until a recent decimation to $100 (involving the alleged imprisonment of the creator of the original devil's flask, for unrelated charges), and perhaps the other is simply selling the bottles for reasonably pricey science demonstrations. Very few manufacturers of Bologna bottles exist today, I could only find one in Germany, and likely they are not eager to help with the spreading of this old knowledge. Another possibility is that every glassblower in the world knows how to make these and simply doesn't because they are perceived dangerous or useless, and it is for this same reason that easily accessible knowledge is not forthcoming.


  1. ^ Cooley, Arnold James (1854). A cyclopaedia of six thousand practical receipts, and collateral information in the arts manufactures, and trades including medicine, pharmacy, and domestic economy: Designed as a compendious book of reference for the manufacturer, tradesman, amateur, and heads of families. D. Appleton & Co.. pp. 124. ISBN N/A. 
  2. ^ The new American cyclopædia, ed. by G. Ripley and C.A. Dana. Beam-Browning. 1859. pp. 450. ISBN N/A. 
  3. ^ Knight, Edward Henry (1876). Knight's American mechanical dictionary: A description of tools, instruments, machines, processes, and engineering; history of inventions; general technological vocabulary; and digest of mechanical appliances in science and the arts. Hurd and Houghton. pp. 110. ISBN N/A. 
  4. ^ The Locomotive, Volume 6. Hartford Steam Broiler Inspection and Insurance Co. 1885. pp. 158. ISBN N/A. 
  5. ^ "1913 Websters Dictionary via". 1913 Websters Dictionary. 
  6. ^ "Bologna Bottles Univ. of Illinois at Urbana-Champaign". UIUC Physics Lecture Demonstration Database. Univ. of Illinois at Urbana-Champaign. Retrieved 1996. 

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