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Thread: Looking for a few answers

  1. #1

    Looking for a few answers

    Hi im new here. So i normally melt aluminium and have a few questiosn that i havent been able to find answers to online. I figured this would be the place to ask.
    So the first one is about melting anodized aluminium. I have a couple of pots that im thinking about melting. From what i understand, anodized aluminium just means more slag. Is this worth melting/should i do anything differently?
    Ive been using plaster as insulation but it cracks easy and i cant melt much more than aluminium. Ive looked into fireclay/firebrick. Is it as simple as adding water to the fireclay? Are there any other long lasting cheap refractories?
    Last question is about silicone as a molding material for lost wax casting. Alginate works nicely for capturing detail on hands for example, and you can slide your hand out. I need to use silicone because it can take the temps of hot wax. Am i going to be able to get my hand out of there?

  2. #2
    Administrator Site Admin
    Join Date
    Dec 2005
    Huatulco, Mexico
    One-third fireclay to two-thirds silica sand makes a decent refractory for aluminum melting. Mi it thoroughly dry and then add just enough water to get it to stick together when you squeeze it into a ball. Then let it sit in a plastic bag for a day or two before you ram it hard into your form.

    That's about as cheap as it comes. Far better is 3000 degree firebrick or a castable refractory that costs about 50 dollars a bag.

    Silicone is a great molding material for lost wax casting, the best in fact. It's expensive though. I mostly use polyurethane which costs about half as much. It does has it drawbacks. For one, whereas silicone won't stick to much of anything but itself, polyurethane is one of the strongest adhesives on Earth. The fumes are respiratory irritants as well, calling for a respirator. If you are molding your hand, I don't know. Most chemical reactions generate a good amount of heat. Go to the Smooth-On web site and do some research.

    When I die, Heaven can wait—I want to go to McMaster-Carr.

  3. #3
    Senior Member
    Join Date
    Jan 2012
    Buffalo, NY
    To add to what Rasper posted, the fireclay will likely remain plastic until it is fired. You will find some really useful information in this tutorial
    The fact that aluminum is anodized isn't nearly as important as the type of alloy or furnace atmosphere in controlling dross. Paint and dirt are pretty major contributors too.

    Welcome to the forum


  4. #4
    Senior Member Wolfcreek-Steve's Avatar
    Join Date
    Apr 2014
    Central Wisconsin
    My advice is don't cast your hand into a urethane mold, there are parting compounds, but you may wear the mold for the rest of your life. (and that's embarrassing) I did a quick search of youtube and silicone and alginate appear to be the materials of choice.
    What is that squeaking noise?

  5. #5
    Thanks for the responses. Just a couple more things
    Is paraffin wax alright for pouring into the silicone? And are sprues absolutely necessary for lost wax casting?
    Also i never really put much thought into this but as long as i dont do it while its snowing and keep molds warm is it safe to melt aluminium during the winter?

  6. #6
    yea, it's safe to do it in the winter, just try to avoid getting any rain or snow on the stuff, expecially ingot molds or your tools when your running the furnace or before it. Water, when molten metal is poured on top of it or if your tool has water on it and you stick it down in the metal could cause a flash steam explosion, which will send molten metal flying everywhere as molten shrapnel, and getting that on you is just asking for a bad day.

    The sprues are there for the air to escape as the metal is being poured in, otherwise it'll want to trap the air and not flow into all of the cavities.

  7. #7
    Keep your furnace dry too, it's not going to like getting fired up from damp every time.
    The only time You're not following your nose is when your going backward!.......Andy (ME) .
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  8. #8
    Senior Member
    Join Date
    Jul 2008
    Suffolk, UK
    For life casting don't use silicone, it can be an irritant with long term contact I'm led to believe. I cast my son's hand in alginate then made a plaster master from it. I was going to make a copy mold from that in silicone but never got around to it.

    Anodised al is usually an extruded or wrought grade which is not best for casting, it will melt and cast if you get a molten heel of metal in the bottom of the crucible first it helps the melt along. Better to find previously cast alloys for melting stock.

  9. #9
    Peedee is on the right track for life casting. Start with an Alginate cast. Fill it with plaster. Then use the plaster master to make the silicone mold. There are some lifecast friendly silicones out there but you need to back them up with a plaster mother mold as they are too expensive and flexable to cast a big block of. There are a bunch of great youtube videos on lifecasting, or hit up Frank over at 's videos on lifecasting, casting sculptors, and hard objects (he does a good job of walking you through step by step, and tells you what products he uses and some others that work).

    Don't go out and try casting someone's head for your first life cast (unless you really don't care for that person...). Start small and get bigger. You will have things that fail, learn from it and get better.


  10. #10
    Alright, thanks.
    I have made a plan for my hand casting which is kind of improvised but i want to run it by to see if there are any major flaws i should know before doing this. So my plan is to have my first negative mold in alginate. Ill pour plaster of paris in the mold, and use an improvised vaccum chamber (vaccum cleaner hose taped tight with a paper bag to the mold container) to get air bubbles out. I plan to have a square cookie cutter kind of thing on top of the alginate so when i pour the plaster, it gives a square base. I take the plaster hand and pour silicon over it (i still have to look into what silicone i should be buying). I watched Franks video and know to cut zigzag to help the silicone not shift. Im semi concerned about the silicone being able to come out in two pieces. I remove the hand and fit the two part mold together in the original container. Here is the issue. So i have paraffin wax which i assume to be ok for lost wax casting, but i dont know. Does it capture good detail? Also I understand the purpose of sprues and gating, but how bad would the end result be if i used none? I dont see many easy ways to make sprues out of paraffin wax and i dont have many power tools to saw off the sprues cleanly afterwards. I would put the wax model in plaster of paris and draw out any bubbles using the vacuum i mentioned earlier. Should i be mixing play sand with the plaster for the mold? I do not have a kiln either. I have a green egg, which can reach 500 degrees. Am i able to burn out all the wax with this? Is 10 hours enough to bake the mold? Id pour the aluminium into the hot mold.
    So thats generally my plan. Does anyone have any advice/suggestions/flaws? Would help a lot.

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