Waxworx 101: Selecting waxes

A primer on using wax in glass casting, Part I

Home>casting, tools & supplies>Waxworx 101a: Selecting waxes

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Wax ain’t just for candles. Surgeons pack bone with it, medievalists seal letters with it, it coats cheeses and shines your car (or your shoes), makes edible Halloween lips and honeycombs and mascara and photocopies and lava lamps and soap and art.

It’s pretty wonderful stuff and, much as I dislike using it, invaluable in glass casting. HOWEVER…it’s daunting, potentially dangerous, and very, very messy, so I thought y’all might appreciate some tips. First off, let’s talk about selecting waxes.

(Typical disclaimer: This is about the waxes I use in MY studio, employing MY casting techniques. I don’t pretend for a minute that this is anything remarkable or unusual…or comprehensive. Please comment if you can add to (or correct) the discussion.)

[dropcap]Lost wax[/dropcap] pretty much explains the role of wax in glass casting: It becomes the model that will be invested (i.e., coated with refractory plaster to make a mold). It’ll then be steamed or burned out of the mold (the “lost” part), leaving a hollow shell you can fill with glass.

The best wax for the job depends on how you engineer your sculpture (and master mold, if you’re using one), its size and level of detail, your working environment, how you plan to get the wax out of the mold, what’s available, and how much you want to spend.

You can buy your wax or mix your own. Waxes can be soft enough to form by hand or so hard you need a lathe or milling machine to carve them. There are about as many types of wax out there as there are sculptures, but they all fall into two categories: Natural or synthetic.

Natural waxes come from animals (beeswax and lanolin, for example) or from plants (Carnauba, soybean wax). Synthetic waxes are man-made, typically derived from petroleum refining.

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Types of wax

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A surprising number of plants and animals produce some type of wax (heck, humans produce earwax but let’s not go there). The big advantage to natural waxes is that they’ll generally burn out in the kiln with little or no residue in the glass. The smoke produced by burning natural wax is far less acrid (and toxic) than microcrystalline waxes, too.

However, natural waxes also tend to be expensive and not really suitable for sculpting. Since they’re produced naturally, you can’t always count on getting exactly the same properties from batch to batch. So natural waxes are more likely to be additives to sculpting wax rather than modeling media by themselves.

Only a few plant-based waxes (that I’m aware of) make an appearance in the sculpting world:

Carnauba (about $14/lb) comes from South American palm trees, although these days there are synthetic varieties, too. Carnauba is very hard and brittle and has one of the highest melting points of any natural wax. It easily takes a high gloss, and is one of the things that gives glossy paper its shine. It’s also used in car wax, cosmetics, food processing, all kinds of stuff.

It’s usually mixed into another wax to harden it and increase gloss, so it’s a nice addition if you’re pouring a wax into a very detailed mold. It will usually increase the melting point of waxes it’s mixed into, which may or may not be a good thing.

Candelilla (about $11/lb) comes from a desert plant of the same name, and is similar to stearin or carnauba in that it glosses up and hardens the wax. It’s not quite as hard and brittle as carnauba, however, and it doesn’t raise the melting point of whatever wax you mix it with. It can also lengthen the working time of your wax, i.e., it can take hours.

Stearin (AKA stearic acid or tristearin, about $10/lb in powder form), another hardener. It’s commonly sold to harden candle wax so it burns longer and stays glossy. It used to be made from beef fat, but now is mostly synthesized from vegetable fats.

Rosin (about $15/lb), hardened pine sap, is typically used on violin bows, in some kinds of polishes, in food products and baseball diamonds. It tends to soften waxes and make them tackier and easier to spread at lower temperatures. The easiest (and usually cheapest) way to obtain it is to buy one of the rosin bags used to improve batters’ and poolplayers’ grips. I’ve used it once or twice to increase the tackiness of wax bondo.

Animal-based waxes can include anything from spermaceti (from whales) to shellac (from a bug) but these have limited application in sculpture. The animal wax you’re most likely to encounter in sculpting is beeswax. It’s typically too hard to work by itself, but it can be used to slightly harden other waxes.

Warning: If you are allergic to bees, be careful when melting beeswax anywhere that insects might have access. I once shot a video of a friend demonstrating a wax technique outside on my back deck. Halfway through, we ran out of victory brown and threw a half-pound of beeswax chunks into the pot. Within 15 minutes, we’d attracted more bees and wasps than I’d seen around my yard all summer. It was hilarious…but it wouldn’t have been quite so funny if one of us had been allergic to bee stings.

I actually don’t use beeswax directly in my casting, but it’s an important part of my recipe for “wax bondo.” (see below)
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Wax “bondo” is what I call a type of home-made filler or “disclosure” wax. It’s a purely organic compound, very sticky, that I use when correcting flaws in a glass casting.

A pound of the stuff costs about $13.60/lb to make. 1 part beeswax to 1 part lard (i.e., Crisco). Put both in the top of a double boiler (or in a metal bowl that you place over a pan of water, being careful NOT to contaminate your mix with water). Heat until completely melted, stirring frequently and NEVER leaving the pot. Pour into a heatproof container and cool.

Bondo feels like a stiffish hand cream (and is REALLY good for your hands; after using it for an hour or two my hands feel silky), and is a creamy yellow color.

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A pate de verre portrait with voids, filled in with wax bondo and ready for recasting.

Its usefulness in casting lies in the fact that it’s entirely organic, and will burn out in the kiln. That means I can pack it into a hole in my casting, coat the whole piece in refractory plaster, and refire. The bondo burns out, leaving a void in the mold that will fill in as the glass softens and moves.

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A flawed pate de verre casting with holes where the glass didn’t quite fit in. I smoothed “wax bondo” into the void, then used a soldering iron to melt the bondo seamlessly into the surface.

When I divest the mold, I’m left with a perfect casting, smudged with what’s left of the bondo. It rubs off easily.

I can pack the bondo onto a casting, then stick the whole thing in the freezer for a couple of hours. The bondo becomes rock-hard, so I can smooth and polish it, blending it into the glass until it’s seamless.

That technique is very useful for joining mismatched casting components into a single whole. Either way, I can coat the entire assemblage, bondo and all, with refractory plaster, add a small reservoir for filler glass if necessary, and refire (recast) the piece.

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The repaired sculpture with the first coat of refractory plaster applied.

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The microcrystalline waxes are by far the most important waxes in sculpture. They are one of the two types of waxes usually derived from petroleum:

  • Macrocrystalline, such as the paraffin wax you buy in the grocery store. These waxes have largish, flattish crystals and tend to be hard and rather brittle, which makes them more difficult to sculpt. (They can be useful in making harder, stiffer waxes, though)
  • Microcrystalline waxes, which (surprise, surprise) are made up of very tiny crystals that make them more elastic than paraffin, as well as denser and stickier.

Most of these waxes are made from refined petroleum; the degree of refinement frequently determines the characteristics of that particular wax. The microcrystallines tend to melt somewhere between 140F and 200F (60C-93C), good working temperatures for sculptors.

They’re readily available through foundry, art and sculpting supply stores, and they can dissolve in petroleum solvents. (which means you can use something like mineral spirits, for example, to clean and polish them)

Microcrystallines are the wax of choice for most sculptores, and foundries call the most common, “victory brown.” (no earthly idea why) They come in varying degrees of hardness, depending on how they were refined.

Typically, the darker the microcrystalline wax, the softer and stickier it is. Victory white is therefore the hardest of these waxes, with the highest melting point. (Usually–I’ve found quite a bit of variability from manufacturer to manufacturer, one reason why I tend to buy a lot of wax at a time.)

Victory brown (I pay about $4.25/lb for a 10-12 lb slab) is nearly black, about the color of very dark chocolate, and soft enough to be worked with the fingers after it sits for a few moments. It will stick to itself (and most anything else) without a lot of work.

It also tends to break off into little crumbs that travel all through the house and stain your clothes, carpets, walls, floors, cats, etc. an oily brown. More about that later.

Amber victory waxes are harder than browns, and more likely to need heat and/or a stickier wax when you’re attaching one piece to another. Victory white wax is harder still. Both cost around $5/lb if you look around.

French red (I pay around $6.75 per pound for an 11-lb slab), one of my favorite waxes, is harder than most of the “victory” waxes, and rather brittle. There are many different forms available; the one I use is a little too brittle for carving but has excellent hardness and takes detail well. It also doesn’t shrink nearly as much as the victory browns when it cools, but some types of it can crack where VB would simply bend.

I like to use it for models that will get a lot of handling. Since it’s more expensive than victory brown, I tend to use it as the outer layer of a model, then fill in with cheaper victory brown.

Hard carving waxes (between $12 and $25 per lb, usually, depending on the type and shape you buy) are used a lot in the jewelry industry and are usually sold in small bars or (for jewelers) special shapes or [tooltip title=”A hard wax, much like a sealing wax, that’s used to attach gemstones to a tool so they can be carved/faceted”]dopping stick[/tooltip]. They are exactly what they sound like: Waxes that are about as hard as alabaster or soapstone, and will take detail perfectly. Some are very brittle; some can be bent.

They’re also very strong, so they’re good for casting smaller pieces with fragile parts, such as a figure with outstretched arms. They have higher melting points than many other waxes, and can be added to soft waxes to strengthen and harden them (if you have a lot of money to spend).

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Water-soluble waxes (about $11/lb) are something new for me. I’ve not yet tried them, but am planning some experiments using them. Chemically, they’re polyethylene glycols, substances that are often used as lubricants in the industrial, food, and pharmaceutical businesses. They dissolve in water, which is their biggest strength.

The jewelry industry uses water-soluble waxes to construct cores inside thin-walled wax models. Jewelers build/cast the soluble wax into a core shape first, and and shape “real” wax on top of that. The assemblage is dunked into water baths for a few minutes to a few hours, so that the soluble wax dissolves, leaving a hollow.

From a working perspective, these waxes are about like paraffin, i.e., lightweight, shapeable and castable but not really suited for hand-sculpting. I’m interested in them as a way to avoid steaming out a mold; if I cast my model from this wax, can I simply immerse the mold in water, dissolve out the wax, and have a clean shell?

Dunno–there are a lot of things to work out first. For one thing, the refractory plaster molds I most often make are themselves degraded by water, so a prolonged water bath isn’t a great idea. OTOH, there ARE other mold refractories that stand up to water (some cements, for example), so it might be possible to construct a shell mold that could be successful with soluble wax.

The question, of course, is whether it’s worth it to go to all that trouble and expense. We’ll see.

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Sculpting wax is a softer wax made specifically for sculpting by hand, like clay. Animators, special effects modelers and some bronze sculptors use it, as it’s less expensive than oil-based clays and can be burned out for lost-wax processes. (I reviewed JF McCaughin’s Sculpting Wax awhile back)

On the plus side, it has a feel similar to oil-based clay. It keeps its shape and doesn’t dry out, which means it stays workable for weeks or months. Most varieties need to be heated enough to be pliable, the way you would Sculpey or oil-based clays (plastilene), and they can be smoothed and polished with a little heat.

They can be chilled if you need them hard enough to give a final polish, and since they’re waterproof you don’t have to worry about damaging or softening them if you get them wet. That can be useful if you use the [tooltip title=”Immersing a model in water and measuring the volume it displaces gives the volume of glass needed for casting it.”]displacement method[/tooltip] to find volumes for casting.

On the minus side, these waxes tend to be expensive. The components that make them sculpt-able can also require prolonged steaming to remove them, which can damage a plaster mold if you’re not careful. And they seem to pick up every bit of grime from your hands (or surroundings); by the time I finish sculpting something with this wax it always looks grubby.

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Wax comes in a few basic form factors:

Slabs are usually the most economical, starting with bars the size of fancy soaps up to 40-pound slabs. Most usually, you’ll find 1-pound bars or billets, and 11-12 pound slabs.

To speed melting (and sometimes just to fit the thing in your wax pot), you’ll need to break up slabs. I’ve tried hot knives, clay wires, saws and just about everything I can think of to chunk up a wax slab.

Easiest way? Stick the whole thing in the freezer. When you need to melt wax, put the whole slab into a heavy-duty garbage bag, take it outside and drop it on a rock three or six times.

The wax will shatter into manageable chunks–just keep whacking it against a hard corner until the pieces are small enough.

Flaked waxes are usually a bit more expensive, but they’re a joy to melt in very precise quantities. You simply open the bag (or carton), pour as much as you need into your wax pot, and seal away the rest. The thin flakes will melt and be ready to use very quickly.

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Prilled beeswax

Granule wax is chunked into small particles, ranging from the size of a coarse sugar crystal to beads 2-4mm across. There are a lot of terms for this, the oddest being “prills” (right). More commonly, red and some types of victory wax can be purchased in beads.

They don’t melt quite as fast as flaked waxes, but they’re still preferable to slabs for quick, precise melting.

Extruded/shapes are most frequently used to sprue models to allow glass to pass in or air to pass out of the mold. They can be extruded hollow or solid, in anything from very hard to very soft waxes.

The jewelry industry offers quite a few pre-made wax shapes, usually for rings and findings, and generally in very hard (carveable) waxes. They can be useful shortcuts, but tend to be more expensive than bulk waxes.

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Picking a wax

Victory brown is my go-to wax, because it’s relatively inexpensive, holds detail, and also can be warmed and worked with the fingers. I personally think it’s a little too soft to use by itself in small, extremely intricate pieces, so I typically add a little paraffin, beeswax and/or French Red to harden it up.

The red-brown mixture also polishes up well, which gives me a flawless surface to invest, and it will tend to protect the model’s surface against casual dings and scratches.

Built/constructed waxes

I’ll use the brown+red wax mix–or victory brown by itself–for large [tooltip title=”A hollow wax model or shell is a time- and money-saver; you use less wax, and the wax steams out faster, reducing potential damage to the mold”]hollow models[/tooltip] that require some assembly, especially where I’m working with lots of curves and soft detail.  In these, I’m frequently bending and attaching sheets of wax to make bases for the piece (which will become the glass reservoirs in the final mold), or hollowing out and reattaching sections of the model.

Harder waxes would need some kind of wax “glue,” to attach, or a lot of additional work to abrade, melt and stick together wax pieces. It’s certainly not difficult to do that, but it’s extra work.

Victory brown is already a bit tacky, so it sticks to itself and makes construction especially easy. The softness of VB means that it doesn’t have much structural integrity, so hollow waxes I build with VB must be at least 1/4 inch thick to stand up to handling, and fragile areas may need to be even thicker.

I do this quite a bit when I’m working from basic shapes, such as a bowl or face; I can make a silicone master mold of the shape I want and then decorate/modify/incorporate it into a new work. VB’s soft tackiness makes modification very easy.

Pouring/casting wax

That’s for constructed models. Poured models, where you pour the wax into a master mold and let it set, require slightly different mixes.

You can pour solid or hollow wax models. For solid models that won’t get a lot of rough handling, I tend to stick with a single wax mix, usually victory brown made a bit harder with 25% French Red.

Small waxes for jewelry

If the model is very small and detailed, such as the models for cast glass pendants at the top of the page, I’ll make very hard, solid models of French Red with additional carnauba or stearin.

They can be tooled or carved if necessary, but mostly I want these guys to be perfectly detailed with no additional hand-sculpting required (because that would add to my costs and this is a pendant, after all), and bulletproof. These guys come out of the mold pretty much ready to be invested, and they can easily be ganged together to save kiln space.

Pouring hollow

I generally pour hollow models using the [tooltip title=”Fill a master mold with hot wax, let it stand for a few minutes, then pour it out, leaving a wax shell behind. You let that cool, and repeat the process until you’ve built up the wax shell.”]“slush” or “slosh”[/tooltip] technique. If I need to extensively work/sculpt the model after pouring, I’ll use all victory brown.

VB makes a softish shell, which can easily be smoothed over and corrected, attached to other models, or even sculpted. Most of the time, though, I’m just going to pour the model as-is, tool and refine it, then polish it and prep for investment.

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This hollow, very detailed model (about 14 inches tall) was made by first sloshing two or three layers of molten French Red wax (with a carnauba hardener) into a silicone master mold. Each time, the wax sat in the mold for a couple of minutes, then I poured it out. When cooled, I sloshed in victory brown to make the softer, stickier (and cheaper) base, to about 3/8 inch thick. The red held the detail well; any pinholes were filled in with wax bondo, and I did some judicious carving to emphasize the smallest details. Then I attached the model to a hollow base that became the beginnings of the glass reservoir in the mold.

For that kind of work, as in the piece at left, I’ll first slosh in two or three layers of French Red, hardened with carnauba and (sometimes) beeswax or stearin.

This ensures the model will take and hold detail very, very well.

French Red has a higher melting point than VB, so once it cools I’ll slosh in slightly thickened VB as filler.

The French Red shell will soften just enough to adhere to the VB, but will fill in the raised areas that need protection while I’m cleaning, polishing and investing the model.

I can still carve into the wax if I need to, with heated tools, and I can fill in any pinholes or defects with bondo.

The French Red takes a very high polish, and steams out very clean.

This is a very looooong post, and I don’t want to make it any more tedious and long-winded than it already is. So…please add your comments/ suggestions/ corrections below, and let me know what else I should be talking about here. Thanks!

2014-07-05T15:19:13+00:00

Comments welcome! (thanks)