# What causes hairline cracks?



## Halver (Feb 24, 2006)

I am new to this.  I found some canning jars that were my grandmothers.  There were no cracks in the jars, but now I see hairline cracks on the surface of one of the jars. The cracks do not go through to the inside. They look like you could flake the glass off the surface. Some of the cracks have double lines and end in the middle of the jar. Can you tell me what causes this?  I have them on top of my cabinets in my kitchen.  Thank you.


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## capsoda (Feb 24, 2006)

Hey Debbie, The extreme temperature changes used in the caning process can cause fine hairline cracks. Also the fermentation process the often happens when exposed to temperature changes while full can cause the same thing.

 There really are many reasons for this occurance. I would suggest displaying them lower away from the ceiling. The temperature changes near the ceiling can cause tiny stress fractures to enlarge to the point of the jar breaking.


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## madpaddla (Feb 24, 2006)

Warren:

 Is that the reason one of the other members of the forum, his bottles were cracking after being displayed for a couple months? ?

 I was wondering the reason for it and if it is preventable.  Thanks 

 Madpaddla


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## capsoda (Feb 24, 2006)

Hey Ben, What it boils down to is temperture and stress. Either will cause cracks under the right conditions.

 At one dump my wife was digging bottles out of the ground faster than I could rinse them and put them in the little bottle bag we use and we heard and watched a hutch soda seperate into halfs. It was pretty weird watching the top half jump off the bottom onto the ground.

 When you dig a bottle with a small stress fracture there is always a chance it will grow and seperate the bottle.


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## madman (Feb 25, 2006)

great info! thanks mike


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## bearswede (Feb 25, 2006)

> What it boils down to is temperture and stress. Either will cause cracks under the right conditions.


 
 And of course, the bottle-making process itself often results in these as well... But those we like to call annealing lines, flashes or heat checks... Anything to avoid the "C" word...


 Ron


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## walkingstick (Feb 25, 2006)

I have found so far this winter that even the temperature change from moving bottles from the truck to the house (-10 to 68 degrees) can cause them cracks to appear.  I am now keeping the bottles wrapped in newspaper inside a cooler and allowing them to warm up slowly about 8 hours inside the house before I even unwrap them.


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## Mihai (Feb 25, 2006)

A few weeks ago I found in river a poison bottle without neck, a kind of light blue but not quite aqua, lovely colour, with some embossing and I took it to have a better look at home. Half way thru, when driving I've heard a cracking noise in the boot of my estate and when home I realized that the bottle poped open. The diffrence from cold water to warm air in the car was too much for an already traumatized bottle.


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## Halver (Feb 25, 2006)

Thank you for all the info.  Do you mean that a bottle should not crack unless there is already a stress fracture?  I always thought canning jars were very strong if they could withstand the canning process.  From my research, I think I have some jars from the late 1800's to the early 1900's.  I would hate to ruin them.  I have put them on lower shelves in my kitchen, but I now plan to put them in my living room.

 Thanks,
 Debbie


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## jarsnstuff (Feb 26, 2006)

Okay, I've had jars displayed on top of my kitchen cabinets for years.  Of course, my home is both air conditioned and heated, so extreme temperatures are very unlikely.  Some of those jars book at around $1000, so if I didn't think they were safe where they are, I'd certainly move them.  (yes, they are securely anchored - I do live in CA!)  When we moved out here, we kept the collection in storage for a couple of years waiting for the house to be built.  The storage facility was not climate controlled, so summer temps were likely well over 100 with winter temps near freezing.  We didn't lose a single jar, even though there were several with small cracks already in them when they went into storage.  It just doesn't make sense to me that jars displayed in the kitchen would develop cracks in them, unless they were very close to a stove, oven or other source of sudden & high heat.  I think there's gotta be something more to this story... -Tammy


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## madpaddla (Feb 26, 2006)

Hello all:

 Seen it also.  I believe what we are talking about is when taking bottles from one temp to the extreme opposite in a short amount of time.  Such as for me, digging a bottle in the winter where the temp in the ground is say 35 and the temp outside after you have dug it is 15 and then to take it home and have it in the house at a temp of 70.  If you dont allow for the bottle to adjust to the surrounding temperatures, any cracks will magnify themselves, and in Mihai case they POP.  Or another example is when the bottle was dug the structure of the bottle seem strong but as they adjust to the new surroundings over time , such as direct sunlight, high humidity, some bottles dont fair as well (due in part to manufacturing meaning that they are not made sturdy.)

 Madpaddla


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## Mihai (Feb 26, 2006)

Hi, 

 When I was young and restless I used to play the chemist. In one of my books I saw how you can cut a bottle in two. You have to tide a string around the bottle, soak the rope in some inflamable liquid, like gas or petrol, and get it alight. When you think is ready just pour some water on it. The shock will crack the bottle on the string line. Apparently. The trick wasn't a full succes for me as most of the times I ended with my kitchen full of shattered glass.

 In that time I also learned that HCl cannot be put in bottles with glass stoppers because the acid attacks the glass and in time the stopper might become stuck. That's why the chloridic acid is the best in cleaning the bottles, it takes a thin lay, probably the already damaged part, from the surface of glass.


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## Halver (Feb 26, 2006)

I have checked the jars above my stove and found no cracks.  The jar that cracked was above the dishwasher and I wonder if steam from opening the dishwasher hit the jar when the kitchen was cold.  There were several other jars in the same place and all are ok, so maybe this one had hairline cracks that I did not notice.

 Debbie


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## capsoda (Feb 26, 2006)

Hey Debbie, It may not happen to every jar but it is likely to happen to a bottle or jar with some kind of defect. Steam and cracks don't go together very well eather.


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## bottleboy311 (Feb 27, 2006)

When I was a kid we use to take glass marbles (cat's eyes), boil them in water, dump the water out and than place them in iced water. The extreme change in tempeture would cause the glass to crack all over the marble. The marble would ussually be intacted but it would look crackled.  Tempeture changes do effect glass. the more the extreme the more damage. 

 Lee


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## capsoda (Feb 27, 2006)

And BB guns too.[]


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