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Thread: Homemade Bronze clay FAILURE! Any ideas what I'm doing wrong?

  1. #1
    Join Date
    Jan 2017
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    Question Homemade Bronze clay FAILURE! Any ideas what I'm doing wrong?

    Good Morning!

    I'm new to metal clay, and experimenting.

    I tied to make my own bronze clay, and it was a dismal failure. I'm hoping the people here can help me figure out why!

    Ingredients (I live in Germany, so sorry for the German language pages :
    Bronzepulver, atomized
    Grain size: 44 microns (325 mesh) irregular
    Melting point: 1083 ° C
    https://www.amazon.de/gp/product/B01...?ie=UTF8&psc=1

    Methylcellulose
    100% pure methyl cellulose E464 Nutritional information: Suitable for vegans and vegetarians, GMO-free, suitable for halal food.
    https://www.amazon.de/gp/product/B01...?ie=UTF8&psc=1

    Recipe:
    ~3 parts bronze powder (3 'scoops')
    ~1 part methylcellulose (1 scoop)
    - Distilled water to powdery clay
    - Massaged with olive oil until workable consistency

    Molding clay. :
    - Made a number of my usual 'test coins'…a small disk about the size and thickness of a quarter…imprinted with a simple pattern.
    - Dried at ~100°F for about 6 hours. Then left sitting overnight at room temp.

    Firing and results:
    I fired the clay with three attempts. Each coin separately.

    1. First coin.
    Fired using the same technique for store-bought PMC3 bronze clay.
    - Large butane torch
    (https://www.amazon.de/gp/product/B00...?ie=UTF8&psc=1)
    - 8 minute timer.
    - Burned off binder for ~1 min
    - Sintered at nice, cherry red glow for 7 mins.
    - Immediately cooled in water (dropped in room temp water)
    - Results: See image one. Coin crumbled like ash No discernable metal sintered.

    2. Second coin.
    Fired using significantly higher heat.
    - Large butane torch
    - 8 minute timer.
    - Burned off binder for ~1 min
    - Sintered at bright orange glow for 7 mins.
    - Immediately cooled in water (dropped in room temp water)
    - Results: See image two. Most of coin disintegrated during sintering. INTERESTING NOTE: Little balls of molten bronze bubbled to surface. Edges of coin appear to have sintered.

    3. Third coin.
    Fired using significantly lower heat.
    - Small butane torch (https://www.amazon.de/Melting-Brazin...c+butane+torch)
    - 8 minute timer.
    - Burned off binder for ~1 min
    - Sintered below any observable heat glow for 7 mins.
    - Immediately cooled in water (dropped in room temp water)
    - Results: See image three. Basically, the same as one. Coin breaks in half easily (easier than breaking the dried clay before hand )

    SOOOOOOOOOO!
    ANY IDEAS WHAT I'M DOING WRONG? WHAT I CAN CHANGE?

    Thanks!
    Attached Thumbnails Attached Thumbnails Try1.jpg   Try2.jpg   Try3.jpg  

  2. #2
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    Romsey
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    I have to say from the outset - I've not tried this and don't work with clay, but kudos for giving it a go.

    My immediate thought is that your butane torch may not be putting out quite enough heat for sintering - the instructions I've seen for torch firing home-made clays say to look for a shimmer. Can you surround the test pieces with firebricks to slow down the heat loss? Also, is there any mileage in oven-drying the pieces to drive off any remaining water?

    There's a number of recipes & ideas here - http://www.metalclayacademy.com/meta...etal-clay.html
    Most of them seem to be kiln-firing for 1 hour for the binder, 2 hours to sinter. I've no real expectation that the DIY clays will respond the same as commercial ones.

  3. #3
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    The torch can get up to about 800°C and, on the second test coin, I think it was too hot. The torch at 7 mins is the firing method I use for the commercial metal clays.

    I am curious however, if the solution for non-commercial metal clays is; lower temp for longer. Maybe in a kiln.

  4. #4
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    Manchester UK
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    I was interested so I had a look on youtube the guy also has some other videos on mixing etc

    Last edited by josef1; 03-03-2017 at 01:20 PM.

  5. #5
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    Thats awesome. Actually, that's where I got my recipe (Actually https://www.youtube.com/watch?v=rXfrOrz2cB8)

    He's using a kiln and I'm using a torch. I'm very curious why the PMC3 commercial bronze is very easily torch-able, and this isn't.

    Although, watching that link again, I looked up my Bronze powder and it is recommended for cold casting (although I can't get the metal content on it).

    I've ordered some different powder from another manufacturer (who does list the content). Maybe it will be better?

    I'll keep the thread posted

  6. #6
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    If it's for cold casting, is it definitely bronze and not a coloured aluminium powder?

  7. #7
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    I absolutely, positively...have no idea I ordered it off of Amazon.de and thanks to my crappy German didn't realize what 'Kaltguss' meant. I've contacted the seller to find out the content.

    In the meantime, I found a metal powder seller I trust who have bronze powder (metal content known) in <45um and 45<X<250um sizes. SO, I'm ordering 100g of each to test

  8. #8
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    Just checked 2 UK sources - both Tiranti & CFS Fibreglass Supplies have COSHH/MSDS sheets indicating that their bronze metal fillers are copper & tin, so definitely bronze, not Al.

    Ease of sintering is going to be down to a couple of issues, not least of which is particle size - I've seen a number of suggestions that a mixture of mesh sizes is preferable.

    Found this, which has a couple of interesting bits - https://web.archive.org/web/20060901.../NL-Fall05.pdf

    Added - forgot about this stuff: http://www.thevirtualfoundry.com/
    Interesting (if you have an FDM printer), but pretty horrendous shrinkage.
    Last edited by ps_bond; 03-03-2017 at 02:49 PM.

  9. #9
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    Very cool links! Thank you for that effort. I'll be reading them tonight!

  10. #10
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    I just wanted to give an update to everyone who had suggestions.

    I've had a bit of SUCCESS!

    1. I got a new metal powder supplier. They sell WATER-ATOMIZED (important) bronze with ~9% tin in both <45um and 75um<X<250um. The clay thats worked (so far) is 1/3 "45um" + 1/3 "250um" + 1/3 methylcellulose. Mixed with distilled water and just a touch of olive oil. Havent tried adding glycerine yet. I discovered from a metallurgy site that the water-atomized (actually non-air-atomized) is important, since tin and copper will oxidize HEAVILY when air atomized. SnO2's melting point is 10x that of of Sn alone. Similar issues with bronze.
    https://www.metallpulver24.de/advanc...e&inc_subcat=1

    2. I bought a camp-stove style burner for torch sintering (no access to a kiln yet. I want to build one, but not in this apartment. Someday)
    https://www.amazon.de/gp/product/B01...?ie=UTF8&psc=1
    It works VERY well. The head spreads the flame out a bit, so I can do wider pieces. Really blows. I measured it to 800°c but felt no need to push the envelope.

    3. I sintered a flat, coin-sized test piece at 730°c (measured by k-style probe) sitting on a steel mesh, with a steel mesh cover and a soft-fire-brick set on top to reduce some of the heat escape for 15 mins (not the usual 7)

    The piece came out hard and bendable (not brittle)...however, the bottom (sitting on the steel mesh) came out with a waffle pattern from softening. Thi would be fine for sculpture but not jewelry. In time, I'll experiment with the times and temps to see if I can prevent that and keep the piece from getting so soft.

    ===
    So, some success. Why all this hassle (besides the interesting fun challenge).

    If you look at the metal powder page, you'll notice that making my bronze clay is about 1/3 the price of buying it. Not so important for small pieces...but larger pieces, this is nice

    Thanks!

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