Casting a 13th century brooch


    This article shows how to make an authentic 13th century annular copper-alloy brooch via the lost-wax method, using common materials found (mostly) around the house. No special tools are required at any stage, including the melting and pouring of the copper-alloy. Many people think that high-temperature casting (ie something other than pewter) has to involve nasty chemical agents, high dollar kilns, and huge torches. Not only will we be using common items, with a little scrounging all the materials will be free.
    Here is a list of the basic tools

    • teaspoon
    • small pocket knife
    • hardwood charcoal or ash
    • tin can
    • compas
    • biscuit tube lid
    • candle wax
    • large Sharpie
    • cheap small paintbrush
    • small candle
    • lighter
    • fine sand
    • fist sized lump of clay
    • small bit of natural fiber rope
    • hairdryer
    • 2 metal salad tongs

    With the exception of the charcoal, clay, and sand, most of these items can be found around the house or the local thrift store. More about where to find these later. For now lets get to creating a model.

    Note that playing with molten metal is dangerous. Anything you do here is done at your own risk. This article is ment for a guide for adults who are smart enough to proceed safely and cautiously. If you don't fall into this category, don't try it.

    Making the wax blanks for carving


    The first step in creating a lost wax casting is creating the wax model. We carve a model in wax that looks just like what we want the finished piece to look like. Modern jewellers use special waxes, however for our purposes, common candle wax is just fine. Find a candle that has a nice dark color (red, green) and is fairly hard (ie you can't bend it much with out it breaking). Melt down a small quantitly of this very carefully over a small flame. Do not overheat or leave unattended as this can cause the wax to catch on fire. If it's starting to smoke, you have it way too hot. Use a metal food can to melt the wax in. You can bend it to form a pour spout and either screw a handle to it or use some pliers to grip it.

    A very convenient mould for our purposes is a flat metal lid with a raised edge from one of the "Cresent Roll" or biscuit tubes. Find one without the raised ribs on it if you can, otherwise simply work the raised areas into your brooch design. Rub some cooking oil/Pam on the lid to prevent the wax from sticking.

    Place the lid on a level surface and carefully pour melted wax into it. Don't overfill it. After it has solidified, place it in the freezer for about 20 minutes. The resulting wax disc should pop right out. Make several of these to play with.

    Carving the model


    Using compass, trace the inner ring of the brooch. You can find the center of the disc by scribing 3 rough arcs of the same radius and seeing where they meet. If you wax blank is larger than you want the brooch to be, trace the outer ring edge as well. Using the pocket knife (or an exacto knife or similar), carefully carve the brooch to shape. You can gently drill a hole in thecenter by rotating the blade point in the center of the disc and carving out from there. The model will get progressivly fragile as you take wax away, however be gentile and you will get good results. In cross section, the brooch can be oval, rectangular, round, or whatever you desire. I prefer a rectangle with slightly rounded sided. You can carve a simple inscription, which was very popular, or some floral designs. Keep it simple for your first one though.

    As a last step, gently carve a notched retainer for the pin. You may leave the center bar a bit big and file it down after casting to reduce the chance of breaking the model.

    Finished Model


    Here is the finished model, carved only with the pocket knife and the compass point (to do the lettering). Special wax carving tools are nice but they are certainly not necessary.



    Now we need a ball of clay about the size of a small fist (about 1 cup full). I have used many types of clay for casting, some purchased at a ceramics supply, some dug from my back yard. I've never seen a huge difference in them as long as you're careful about choosing a pure clay without a lot of inclusions (small rocks etc). If you can't find any clay naturally, ask a local ceramics shop or college ceramics instructor if you can have a handful of stoneware or terra-cotta. Explain what you are doing to them. Most artisans are happy to help a fellow craftsman with an interesting project.

    Sprue Mould


    When you have your clay, take a small lump and make a ball. With the back end of your Sharpie, make a cone-like depression about 1 1/2" deep. This is the mould to make your sprue. The sprue is the ingate for metal to flow into your mould and to act as a reserve for molten metal as your piece cools and shrinks.

    Pouring wax into the sprue mould


    Carefully pour melted wax into this mould. You do not need to let the clay dry at all. When it has cooled and solidified, remove it from the clay and scrape the clay off of it and bring it to about a 1/4" flat point by scraping it gently with the knife. Do not get wax particles mixed into your clay. Be sure and pick out any dribbles that adheres to it after pouring the sprue.

    Notch the sprue


    Cut a small notch on one side of your sprue at the end of the point. While it is not entirely necessary and will be harder to clean off afterwards, it will help the novice attach the sprue to the model much easier.

    Position sprue


    Rest your model back side up on a few wax blanks or similar so that you can position the sprue point level with the model (see image).

    Attach the sprue to the model


    Light the small candle and heat the pointed metal end of the compas (move the pencil end out of the way). It should be hot enough to melt wax. Take a piece of wax and touch it to the point. It should melt and form a drop of wax. Use this to fuse or weld the sprue to the model. You may wish to practice this. Make sure you get good penitration. All joints should be nicely fused together. When the top half of the joint is fused, carefully turn it over and do the same on the front. Try to join it at a spot that will be easy to clean up later, and try to do it directly opposite the notch for the pin.

    First Layer


    With the model made, we now turn our attention to the first layer of our clay mould. Layer 1 must be very fine to pick up detail in the model, it must resist shrinkage so it doesnt crack when it dries, and it must adhere properly to the wax. An excellent formula for this is 1 part finely sifted ash or powdered charcoal, 1 part clay. In recent experiments, we have found the ash to be slightly better at picking up detail.

    Prepare the mix


    If you wish to use charcoal, prepare about a teaspoon full by rubbing to pieces of hardwood (lump) charcoal (not briquets!) together. Collect the powder, and further grind it up using the back of the spoon. Lump charcoal can be purchased at Walmart fairly inexpensively (about $6 for a 10lb bag), or you can scrounge it from fireplaces, bonfires, etc.

    If you wish to use ash, the best kind are wash ashes left over from soapmaking (being part of a reinactment group, you chances of actually knowing a soap maker are much higher than normal). Otherwise, ashes from a hardwood fire that have been finely sifted also work.

    Mix up layer 1


    Mix the powdered charcoal with an equal amout of clay, adding tiny amouts of water until you get a thick paste, roughly the consistancy of Elmers glue. Make sure all the clay lumps are dissolved.

    Paint it black


    Brush on a thin layer of fine ash on the model. Make sure it gets all over. This breaks the surface tension and allows the mix to stick.Next, paint a thin layer of your mix onto the model. Make sure you work it into the details. Don't worry about too thin a coverage, just make sure all the crevaces are filled and that every surface has a thin layer. When this has dried, add more layers until you have 3 or 4. You should end up with a nice coat about 1/16" thick all around. Let this dry for a few hours.

    If it cracks badly on drying, add a bit more charcoal and recoat.

    Gather the sand


    Collect about a handful of fine sand. This can often be found naturally, however avoid beach sand which may contain shell bits. These retain moisture and can crack your mould on firing. Make sure the sand is free from rocks and such. You can optionally sift it with a common kitchen flour sifter.

    Disclosing the usage of the flour sifter to the kitchen overseer is left up to the individual...
    "Why is there sand in my biscuits?"



    In order to keep our outer layer of clay from cracking as it shrinks around our unyielding wax model, it must contain short fibers to lock it together. Traditionally this was horse dung (cow dung does not contain the same long fibers as horse dung). Pyrotechnia also mentions wool clippings. In actuality, dung works the best for this, however a good substitute is sisal rope fibers. Cut them into 1/4" lengths. This length is proportional to your model size. If many cracks develop on larger models try increasing the fiber length, however this generally does not become a factor until you have something several inches in diameter.

    Ingredients for Layer 2


    Here are the ingredients for the coarse layers, by volume:

    • 2 parts clay
    • 3 parts fine sand
    • 3 parts ground pre-fired clay (chamotte), molochite, or more sand if you can't find any of those
    • 2 parts fiber

    The background of a funeral home advertisement was not intentional.

    Mix it up


    Mix the ingredients with enough water to make a paste. It needs to be fluid enough to daub onto the model, yet firm enough not to fall apart, and not so wet that it dissolves the previous layer.

    If you want to dip it on instead of brushing, make it just a little runnier.

    Apply Layer 2


    Lay down a piece of wax paper and begin coating your model with the Layer 2 mixture. Tap it down with the brush to ensure good contact, and make sure there are no voids. This is especially important around the sides. We will do several coats. Wait until the first coat is stable (will hold it's shape) before turning it over for the next coat.

    You can also lay down a pad of mix and make a slurry on the surface, then press them model gently into it, however you must be very careful it doesnt break. This step is the make-or-break, literally, of the process and the one most students find the most difficulty with.

    It is also feasible to dip the model in the mix. Just make the mix a little more fluid, and be sure to brush it a little bit to make sure there are no air bubbles.

    Keep layering


    Continue to add layers, building it up to between 1/8" and 1/4". By the second or third layer you can bridge the gap inside the circle. Make sure the edges of the sprue opening are nice and thick or they will crumble off when we go to pour the metal.

    When you have sufficient layers on, set it aside to dry. Idealy on a wire rack so that air can flow around it and dry evenly. Otherwise, prop it up on some pencils or something. If it drys unevenly it may warp.


    Drying and Firing


    After air drying for about 2 days -- enough to where it's visibly dry -- your model may be burnt out and fired. A small torch can be used to gently melt the wax out of the sprue, then it is set in a small naturally aspirated charcoal fire, sprue down, and fired for about 2 hours at a dull red heat.

    A small pinch-pot crucible can be made from 1 part clay and 2 parts fine sand, coated in ash and left to dry. This will last for several melts usually. You can pre-fire it or just set it in the hearth unfired and use it straight away.

    A small hearth for firing can be made using firebricks with a small opening in the front for air, which can be supplied by a hair dryer.

    Instructions for firing and casting may be found in the casting class notes.