Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 25

Thread: sheet silver cracked apart - any idea why?

  1. #11
    Join Date
    Oct 2009
    Location
    Cumbria
    Posts
    115

    Default

    Now you're gonna blind me with science Peter - lol

    I've just spoken to Cookson and they asked me to send back the sheet to be tested. The guy I spoke to did say he thought it was unlikely that I had over annealed it but will wait and see what the tests reveal.

    Just thinking aloud - surely when doing several solder joints on one piece, its like annealing several times without actually working in between? so in theory, this could happen to something like say a ring that has had several joints soldered, and maybe a bezel cup soldered onto it. During each soldering process the metal is getting as hot as when I am annealing?

  2. #12
    Join Date
    Dec 2009
    Location
    Central London
    Posts
    8,845

    Default

    Faith,
    There is a lot of logic in what you say, but you can't reason with a piece of metal, so I am waiting with baited breath for the final answer. Kind regards, Dennis.

  3. #13
    Join Date
    Jun 2010
    Posts
    313

    Default

    Nooo, don't listen to Faith Peter, I want the techy stuff!!

    I've only ever had this happen with sheet that was contaminated in my own melt-pot. Very unlikely with Cookies sheet, but if it's going to happen with a supplier, it's better with a big company like Cookies who'll review and replace rather than fob you off.

    I can't think of any reason why it might have happened with sterling in this shape. Please press Cookies to tell us what testing they did when they reply, we're really interested, not in a critical way.

  4. #14
    Join Date
    Aug 2009
    Location
    Staffordshire
    Posts
    1,727

    Default

    I agree with Joe, press Cookies for an answer Faith. It would be really good from a learning perspective to understand why this has happened.

  5. #15
    Join Date
    Jul 2009
    Location
    Romsey
    Posts
    5,256

    Default

    OK, the brief version from Brepohl is that excessive grain growth causes mechanically weak metal which can crack (either working or quenching too fast).

    Excessive grain growth through annealing is usually caused by 1 or more of the following 4 factors:

    Insufficient working of the metal prior to annealing.
    Heating to annealing temperature too slowly.
    Holding at annealing heat too long.
    Heating too high.

    Fundamentally, as you work the metal - as Dennis has said - you are distorting the grains, or crystals. They can take a certain amount of distortion, causing the grain boundaries to become progressively more stressed, until any attempt at further deformation will result in the metal cracking (where the stress in the grain boundaries has become too much for the grains to hold together). So, we anneal - this involves taking the metal up to a point where the grains can recrystallise, relaxing the strain on the grain boundaries, coupled with a small amount of grain growth; time & temperature have to be more-or-less right to get the metal to the state we want it to, but if it wasn't worked enough beforehand, you don't have the stressed structure to work with so you are only really going to encourage excessive grain growth.

    Brepohl's much more thorough than that - hope it wasn't too over-tech!

    That said, as you've got the offer to have the metal tested I'd go for it - but that looks like you've got firestain in the picture?

  6. #16
    Join Date
    Jan 2010
    Location
    Southampton, UK
    Posts
    128

    Default

    A student of mine had something similar happen when he was soldering a big piece of silver. Essentially the soldering didn't work as he wasn't using a large enough flame. He tried again and again (at home btw not in class where I could have seen what was going on and helped!), each time heating the silver up too slowly, only up to about annealing temperature rather than the temperature needed for soldering, and after about the fifth attempt it cracked - a very expensive lesson for him! The reasons for the cracking were two of the factors that Peter listed -
    Heating to annealing temperature too slowly.
    Holding at annealing heat too long.
    Jo
    Daisychain Jewellery - Handcrafted sterling silver jewellery and jewellery tuition
    www.daisychainjewellery.co.uk
    www.daisychaindesignsjewellery.blogspot.com

  7. #17
    Join Date
    Oct 2009
    Location
    Cumbria
    Posts
    115

    Default

    Crikey, with all the things that need to be just about right - its a wonder I havent buggered it up before now then!

    The sheet went back to Cookson today so hopefully I will find out the bad news soon.

  8. #18
    Join Date
    Dec 2009
    Location
    Central London
    Posts
    8,845

    Default

    Quote Originally Posted by abyjem View Post
    Crikey, with all the things that need to be just about right - its a wonder I havent buggered it up before now then!
    And so say all of us, us ,us. Dennis.

  9. #19
    Join Date
    Nov 2010
    Posts
    9

    Default

    Take a piece of thin plastic and bend it back and forth and you will see that it starts to go white then eventually breaks. This is what has happened in essence to your sheet silver, the "grain" structure has been adversely affected by repeated "working" , both physical and through energy changes (heat / cold) during the annealing process. Eventually it will happen, everything has a life span Also remember that the Silver sheet will be alloyed with some other element that will have contributed.

    cheers,
    Ruby

  10. #20
    Join Date
    Oct 2009
    Location
    Cumbria
    Posts
    115

    Default

    Thanks Peter - I rather take exception to my post being hijacked, especially by spam for a naff website!

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •