Results 1 to 10 of 17

Thread: Black oxide on silver after melting

Hybrid View

Previous Post Previous Post   Next Post Next Post
  1. #1
    Join Date
    Jul 2022
    Posts
    21

    Default Black oxide on silver after melting

    Hello everybody,
    when I pour molten silver (I usually use 800 silver) and pour it into plaster cylinders for lost wax casting, the silver oxidizes and becomes dark in color similar to black. Conversely, when I pour the silver into the sand casting mold (delft clay) the silver after it has cooled has a light yellow color without showing all that oxide that instead occurs in the other type of casting. I can't understand why this black oxide occurs and how to do to prevent this from happening. I state that I use a melting furnace with graphite crucibles and I use borax. Thanks in advance for your help.
    Attached Thumbnails Attached Thumbnails photo_2022-07-18_11-47-45.jpg   photo_2022-07-18_11-47-46.jpg  

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

    Default

    Unlike sand, casting investment contains sulphur, so its no wonder that the surface of your casting is black with sulphides, both of silver, and the 20% base metals contained in your alloy.
    However this should present no problem, as it would easily dissolve in warm safety pickle, or diluted sulphuric acid.
    Dennis.

  3. #3
    Join Date
    Jul 2022
    Posts
    21

    Default

    Quote Originally Posted by Dennis View Post
    Unlike sand, casting investment contains sulphur, so its no wonder that the surface of your casting is black with sulphides, both of silver, and the 20% base metals contained in your alloy.
    However this should present no problem, as it would easily dissolve in warm safety pickle, or diluted sulphuric acid.
    Dennis.
    Seeing some videos on youtube, why for many silversmiths the melting of the silver inside the flasks is not oxidized but the silver is clear immediately after the breaking of the plaster coating inside the water?

  4. #4
    Join Date
    Dec 2009
    Location
    Central London
    Posts
    8,845

    Default

    Don't know, but keep an eye on this space, because there will be more answers in a week or two. Dennis.

  5. #5
    Join Date
    Jul 2022
    Posts
    21

    Default

    Quote Originally Posted by Dennis View Post
    Don't know, but keep an eye on this space, because there will be more answers in a week or two. Dennis.
    Thanks Dennis for your reply, I will be waiting for any other replies

  6. #6
    Join Date
    Feb 2011
    Location
    Scotland
    Posts
    3,392

    Default

    I did answer last night but it seems to have disappeared!
    Not my area of expertise but I doubt anyone can explain the different outcomes you’ve found on YouTube videos by other silversmith.
    I did wonder as your silver is only 80% pure in terms of the 925 we are used to if the other alloys are causing the oxidisation?

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
  •