Editor's Note: This is the second article in a two-part series on wax carving by master model maker, designer, and educator Kate Wolf of Wolf Designs in Portland, Maine, who recently launched a new line of waxes and wax carving tools ( www.WolfWax.com ). This month Kate shares techniques and tips for calculating thickness and shrinkage, hollowing, finishing, and more. In addition, she offers the second half of a visual tour through the step-by-step carving of a ring with a pear-shaped center stone.

Lost Wax
When creating a one-of-a-kind piece, I usually take a cold RTV (room temperature vulcanizing) mold of the master wax pattern, inject wax into the mold, and cast the injected wax. Although you can count on the master wax pattern getting damaged in the molding process, doing this is good insurance against a possible failed casting. Afterward, you can modify and cast the master wax pattern, or mold it again.

If you'd like to make multiple pieces, you can use the casting as your master model. By detailing the master model and taking a rubber or metal mold of it, you can then inject additional waxes into the mold and cast them.

Sometimes, usually in the case of rings where a range of sizes is required, you need to make a second generation of models from the original master model for each ring size. These are called production models.

Shrinkage
There are many variables that determine the degree to which shrinkage will affect the final product. These variables include wax thickness, size, and form; whether the piece will be molded and how many times it will be molded; type of mold; type of wax; vulcanization method; and injection pressures and temperatures. As a general rule, most model makers count on one to 12 percent shrinkage, depending on the scenario. Here are some examples of the shrinkage I plan for in most of my model work:

• Cast wax directly and finish casting (one-of-a-kind) = 1 percent

• Cast wax directly, detail metal casting, take vulcanized rubber mold, then cast injected wax from mold = 4 percent

• Take RTV mold of wax, cast injected wax, detail metal casting, make vulcanized rubber mold, then cast wax injected from vulcanized mold = 5 percent   

• For production models of rings where multiple sizes are needed, take RTV mold of wax, cast injected wax, detail metal casting, make vulcanized rubber mold, inject waxes (size either injected waxes or the new castings), detail sized castings, make vulcanized production molds = 9 percent

That being said, your variables and shrinkage percentages will differ from mine. This is where the SWAG method comes in handy: Make a Scientific Wild Ass Guess as to what your shrinkage will be. (If you are not doing your own casting, by all means ask your caster what shrinkages to expect.) Take notes, track your results, and adjust accordingly. (For additional methods for calculating shrinkage rates, see "A Model Approach," by Gregg Todd, August 2002 MJSA Journal.)

I use a digital millimeter gauge to make shrinkage calculations for overall dimensions. When making master models for pieces that include stones, I put aside the millimeter gauge and rely on my experienced eye to ensure an accurate fit for the stones.

When carving waxes for pieces that include bezel-set stones, I used to carve the outside dimensions of a bezel first, and then cut the seat for the stone. This technique produced an inaccurate fit, as the walls flexed slightly when the stone was pressed into the wax bezel. Once the piece was cast, the walls didn't flex and the stone didn't fit unless I ground away the inside of the bezel. Now I leave a mass of wax around the outside of the bezel until the center stone is seated and fits well. Then I file and scrape the excess wax from the outside of the bezel.

For a one-of-a-kind piece, I suggest making the stone fit in without any gaps, but not too tight. Examine the inside walls of the bezel for scrape marks made by the stone being pushed into and pulled out of the bezel. Open up the bezel at these scrape marks. Repeat putting the stone into the bezel and removing wax at the scrape marks until the stone fits without marking the inside bezel walls.

For wax models that are to be cast and then produced from a vulcanized rubber mold, allow the stone some wiggle room. Open up the bezel about four percent larger than perfect fit. (I don't rely on the millimeter gauge for this, but have learned to trust my eye.)

If the bezel has been opened up too far, I wait until the very end of the project, then flow a bit of molten touch-up wax inside the bezel. This wax is much softer than carving wax and can be built up and scraped smooth with ease.

Thickness
As with shrinkage, there are numerous variables that determine the ideal thickness of a wax model. They include size, metal to be used for casting, stone settings, function, and whether the piece is one-of-a-kind or a production model. Generally speaking, one-of-a-kind pieces may be thinner than a piece that will be molded. It is easier to cast a piece in metal than it is to get a good wax injection of a piece from a mold. Therefore, I rarely make master models less than a millimeter thick.

Progressive Solidification
When carving a wax, it is important to keep the concept of progressive solidification in mind. When molten metal fills the investment cavity left by your wax pattern, the metal solidifies from the outside surfaces inward. The metal shrinks as it solidifies. As it shrinks, any metal that is still liquid is drawn in to replace the diminished volume.

Considering progressive solidification, an ideal wax pattern will be heaviest at the sprue connection. There should be a gradual transition to the thinnest part of the wax pattern, which is located furthest from the sprue. (A model example is a tree, which graduates in thickness from leaves to twigs to branches to trunk.) If you have carved a wax that has abrupt transitions from thin to thick, the thin areas will freeze first, blocking the flow of molten metal to the still-shrinking thicker areas. This situation will result in shrinkage porosity.

Repose
Everyone has a good eye; many of us just don't realize it. When a student shows me his or her work in progress, and we both know something is not right, I ask, "Where is your eye being pulled?" The student focuses in on the exact same thing that is distracting me-always. In my 14 years of teaching this has never failed.

I then ask, "Why is your eye being pulled to that spot?" and "What needs to be resolved there?" The student points out a nice sweeping curve that has an awkward flat spot, or one side of the shank that is heavier than the other, or the top of a bezel that isn't level.

When something about the design or form needs to be resolved, it creates a visual tension that is compelling. Often, when you resolve whatever it is that causes this visual tension, there is another area that begs for help. It is essential to keep working around the piece until your eye takes in the entire form and is at rest. This state of visual inactivity is called repose.

Hollowing
When the outside of the piece is resolved, it's time to hollow it out, if you so desire. Hollowing is often the step that you rush through and regret later. Because it's easier to hollow out a wax than it is to hollow out a metal model, it's easy to remove too much material.

To hollow correctly, start by removing the bulk of the material with wax burs. Then scrape the inside surfaces of the wax model smooth with scraping tools that match the desired contours.   Use a spring gauge to check for wall thickness. Once you have an area that is of a desired thickness, take note of the shade of the wax and use this color as a guideline for hollowing. When possible, hollow the inside corners to a rounded radius. This allows the metal to flow easier, and helps avoid turbulence as the molten metal fills the investment cavity.

On a ring similar to the one used in the step-by-step project shown here, I hollow out the piece to the following proportions (which honor the concept of progressive solidification): The bottom of the shank (where the sprue will be attached) is the thickest part of the ring at 2 mm. The shank gradually tapers to the top, which measures 1 mm. This 1 mm thickness makes it easier to do the pierce out work for the windows.

Piercing
Once the piece is hollowed, it's time to do any necessary piercing work. It is much easier to cut clean windows from wax that is 1 mm thick than from thicker wax. (I will use the project illustrated in this article as an example when describing piercing. See the detailed photos on this page for a visual reference.)

Begin by drilling pilot holes in the areas to be pierced. Pull the drill bit around to remove some of the excess material from the windows. Use a small, sharp knife to relieve the corners, making 45 degree cuts from the scribed corners to the pilot hole. These stop cuts make it easier to open up the windows without overcutting.

Use a small knife to open up the windows. Move from corner to corner in a clockwise and then counter-clockwise direction. Repeat relieving the corners, this time at a 90 degree angle, and open up the windows until they are neat and precise. Use a tapered triangle tool to shave from side to side, leaving smooth, flat edges and crisp corners.

Since pierced out areas will be filled with investment, avoid carving windows that come to a long, sharp taper. When the molten metal enters the investment cavity, it can cause these sharp points of investment to break off and float on the molten metal stream, causing investment inclusions. To avoid this, leave the corners of these windows rounded, and scrape a sharp V onto the surface of the wax to give the illusion of a taper.

Finishing
There are no miracles in the casting process. If there are cracks, pits, trapped air bubbles, or other imperfections in the wax model, you can count on them becoming investment inclusions in the casting. What you see when examining the wax model, with the aid of good lighting and magnification, is what you'll get in the finished casting. Spending a few extra minutes refining the wax model can save frustrating hours of detailing the metal casting.

When finishing models that are organic looking or have curvilinear forms, I use a felt stick to smooth away the tool marks. Other model makers use a piece of nylon stocking or silk. You can also use a solvent, such as Wax Brite or Wax Kleen, to help dissolve the surface of the wax and smooth it. Be sure to rinse off the excess solvent or it will continue to erode the surface of the wax. For best results, use felt sticks, wax solvent, and any other finishing techniques before using touch-up wax, as these processes will erode the softer wax faster than the harder carving wax, resulting in an uneven surface.

Be very careful if flame polishing. I avoid this technique unless it is used on patterns that I have cut intentionally to be rounded out with a flame.

For geometric forms, I don't polish the wax or use solvents because I don't want to lose the crisp edges. Instead, I go over all surfaces with scraping tools, using light, overlapping strokes.

Touch-up
Touch-up wax is ideal for filling in surface imperfections on carving wax, such as pits and hairline cracks. This wax is liquid at approximately 165°F/74°C and is designed to flow easily. Since touch-up wax is soft and weak, it is not ideal for repairs that need to be durable, such as attaching a shank to a ring. Unlike working with build-up wax, it is not necessary to melt the wax pattern when applying touch-up wax.

Phew!
The final and most important piece of advice I can offer is don't be afraid to make mistakes-they are the only way we learn. Mistakes teach us to problem solve.

Also, it's very helpful to work on a few pieces at a time, so when you get stuck, you can work on another piece. As you do, your subconscious often gives you the answers you need for the first project. This also helps you to come back to the work in progress with fresh eyes.

So just go for it: Carve a pound of wax, explore the material, make mistakes, get lost in the process, and have fun. Just cut loose!