Wednesday, August 22, 2012

Cuttlebone Casting Part II - Model and Mold Preparation

Good Morning,

Wednesday's are devoted to what's happening in the studio here at The Alchemists Vessel, and this morning is Part II of the three part series, Cuttlebone Casting.

Monday we discussed materials and the very basics of beginning to model and mold the pendant.  Today we are going to continue the project with making the model and creating the mold itself.

If you would like to follow along, I recommend a quick review of Monday's post, Cuttlebone Casting Part I- Materials and Model Making.

Pin or Sharp Pointy Object
Modeling (Jeweler's) Wax
Flat File
Jeweler's Saw
Lighter Fluid
Soft Cloth
Brass Rods
Unsharpened Pencil
Prepared Cuttlebone halves

Last time the design of the piece was decided upon, sketched and cut out.  The sample project shown throughout the instruction will be  simple Cross shape.

This is about 1-1/2" tall x 1-1/4" wide.  Sketched in pencil (then traced with ink for a clearer photo), cut out of the paper, this will be the Paper Template from which to trace or "scribe" the design on to the wax block.


Cut out and place your Paper Template on top of the modeling wax and with a pin or other sharp object draw or “scribe” your design into the wax.  Trace the template.  Below is a T-pin, which I use to scribe the design in to the wax.

Note: You can see that the template is a little too long for the wax, you may adjust your design to fit with in the wax area before your trace the design.

Next with a Jeweler’s Saw and a Spiral saw blade (these cut modeling wax best, and straight blades work just fine, too) cut out your model.

Here is the beginning of the wax model.  Using a straight saw blade the block has been cut along the scribed lines in the wax.  Once completely cut out the model will be ready for final preparations.

Once your model is cut out, use a wax file to smooth and true the edges up, keeping them straight and even.  They make specific files for wax, if one is not available a flat jewelers / craft file will work as well.

Using a tiny bit of lighter fluid and a soft cloth, smooth out the surface, corners, and sides of the model.  This will remove any imperfections, nicks and scratches, and smooth the surface for a better impression.  Remember every imperfection will transfer to the finished product.  Be careful, over working the wax will distort or destroy any detail you may have carved into the model.

I have drilled tiny pilot holes in my design, the center hole will house the gemstone, and the others are to keep the design consistent.

NOTE:  I failed to take a picture prior to completing the next steps.  What you see here, is the final model, after it has been pressed into the cuttlebone halves.  The white material is dust from the bone.   Also, I dropped it, as I mentioned the wax is very brittle and I managed to break the arm of the Cross on one side.  However this happened after creating the mold impression!

Whew!  Almost there!


Now the fun starts!  Using one side of your cuttlebone, press your model into the flat surface of the bone.  The bone is soft, use gentle even pressure.  Next place the other half of the cuttlebone on top of the wax model and other half of the bone-mold and press the two sides together.  GENTLY!  If you press too hard the cuttlebone will break and another one will have to be prepared before continuing.  The wax model is now embedded in the cuttlebone.  It does take some pressure, and you can hear the model sinking into the surface of the cuttlebone.  The halves do need to touch, but press the wax into them enough for a well-defined impression.

With a pencil, mark several places on the outside of the bone so you can align the halves later.  This is important, the sides of the mold must match up for the inside to cast properly.

Remove the model.  The impression will be left behind.  This model may be used again to make another mold.

Here you can see the impression the wax model has made in the bone, along with the natural striated patterns of the bone itself, they are distorted by the the impression of the cross.  (The other side of the cuttlebone looks just like this).

If desired, very, very carefully sand the impression for better definition.  Do not overwork the area or you can distort the impression.


Choosing one side of the mold, lay it flat and using the end of a pencil (not sharpened) create a SPRUE CHANNEL by gently pressing the pencil into the bone, just above and at the edge of the impression.  What’s a sprue channel?  It is a channel that allows the material you’re pouring to enter the mold for casting.  Make sure that this just touches the edge or of your model impression, but not so much to distort your design.  (Simon didn’t say to remove the pencil).

Next using brass rods or something with a smaller diameter than the pencil create VENT GATES.  What’s a vent gate?  It is a channel that will allow air to escape the mold during the casting process.  Just like you did with the pencil, using two (2) Brass rods (or tool) lay them just at the end and edge of the arms of the Cross.  These should also just touch the edge of the impression.  With the pencil and then the rods in place, place the second half of your mold over the pencil and rods and press down, keeping in mind to align the pencil marks on the outside of the cuttlebone.  The channels must be created in both sides of the mold.  Take the halves apart, remove the pencil and rods.

Are you still with me?  Still want to make a piece of jewelry?   Alrighty then!  Here we go!

Now match up the halves with the lines you made on the outside.  Find the Sprue Channel. Very carefully mark the top of the mold (both sides), on either side of the Sprue Channel.  This is where you will cut the SPRUE HOLE.  What’s a sprue hole?  It is a larger opening in the mold, which allows you to pour material into the Sprue Channel and into the mold.  This makes it easier to pour the material from whatever you have melted your material in, into the mold itself.  If you try to aim for the Sprue Channel you will wind up with material on the outside of the mold and possibly severe burns.  Molten Metal is HOT HOT HOT!  This project only gets up to about 400 degrees, but that can still do some serious damage!  Be careful.

Here you can see the Vent Gates, Sprue Hole, Sprue Channel, and the pencil marks I made on the outside of the bone to align the pieces.

Now align the Mold again.  Using Mold Wire, Rubber bands, or other type of binding (I do not recommend Duct Tape or other adhesive strips or bindings), match up the halves and secure (close) the mold.

The photo above is the closed mold, with Rubber band binding.

You just made a mold.  COOL!


Set the mold aside, some place safe and dry.

The preparations are now done and the mold is ready to begin casting the piece.

Take a break, have a little sit down and enjoy some tea, coffee, a beverage, or snack of your choice!  You've earned it!

Next time.  Part III - Casting the piece. 

Thank you for stopping by and having a look.

The Alchemists Vessel would like to wish you a pleasant Wednesday.

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