Smudges = Divit?

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  • #9618
    Kingbingo1
    Participant

    I just finished a piece and there are small cloudy marks, similar to light smudges on it.  This appears mostly on my blue pieces.  Is it divit?  Someone mentioned fine sandpaper, but it scratches the glass.  Will the Fire polishing get rid of the scratches?

    #12016
    Stephen Richard
    Participant

    Yes this sounds like the most usual form of devitrification.

    The best way to deal with it is to prevent it.  Very good cleaning without additives and polishing dry are the best ways of preventing it.

    http://glasstips.blogspot.com/2010/08/cleaning-glass.html

     

    In firing you need to go quickly through the devit range ca. 670C to 750C both up and down.

     

    Abrasion of the surface whether with sandpaper or sandblasting will deal with the devit, but leave fine scratches.  These can be removed by firing to fire polishing temperatures.  You will need to go slower on the heat up than originally.  Once you are about 50C above the annealing temp, you can go fast to the fire polish with only a very, very short soak, then down to anneal soak and cool.

    http://glasstips.blogspot.com/2011/02/fire-polishing.html

    http://glasstips.blogspot.com/2009/08/polishing-kiln-fired-glass.html

    Another way to deal with the devit is to apply a devit solution, such as borax or one of the branded products take the piece to fire polish and anneal.

    Stephen Richard

    blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

    #12017
    Kingbingo1
    Participant

    I appreciate the assistance.  I wash the glass with hot water, then wipe dry with a clean cloth.  Then I use a window cleaner to finish it off.  Is a Window cleaner okay or should  use something else?

    #12018
    Stephen Richard
    Participant

    Why after cleaning and polishing dry do you then apply a product that may contain a number of additives?  Don’t use a commercial window cleaner, as they contain a number of additives, some of which promote devitrification.  So just stop when it is clean, don’t add chemicals.

    Stephen Richard

    blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

    #12019
    siggy
    Participant

    I am experimenting with fusing glass knobs for my kitchen cabinets.  Does anyone know of a way to polish them to a sheen after firing.  The surface appears cloudy.  Is there a diamond type sander/buffer that I can purchase?

    #12020
    Stephen Richard
    Participant

    See my comments earlier in this thread.

     

    Stephen Richard

    blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

    #12021
    siggy
    Participant

    Hi,

    I guess I forgot to mention that they were made in a stainless mold so the fire polishing method probably won’t work because they will lose their rounded dome shape. I am going to attempt to hand polish using cerium polishing pads.

    #12022
    Stephen Richard
    Participant

    So the dome part was down in the mould?

    Yes you need to get all the separator off.  If it is a simple domed piece, you can fire polish it.  Take it up to about 50C above the annealing point slowly, maybe only 50C/hr.  Then go really fast up to about 740-760C (you will have to peek to determine when the surface becomes shiny again) and then proceed to the normal annealing schedule.

    Stephen Richard

    blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

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