A Technique for Dopping with Black Wax
by Bob Keller
When I began faceting I was taught to dop using wax, and I still use it. Wax is fast, cheap, it works, and it is not difficult to use, although I might be of a different opinion had I not been introduced through demonstrations to the process by another faceter who was proficient with wax dopping.
I use a black wax which is sold by the Graves Company as item 13-062 in their catalog. It is inexpensive at 4 sticks (1 lb.) for $8.50. There's enough wax in one stick to dop many faceted stones. I find the 1/4 lb. sticks are unwieldy to manipulate and work with due to their size, so I cut them up into handier sized pieces prior to use.
The melting temperature is given as 165 degrees F. and this technique uses the wax heated to a liquid state. Of course it may not be suitable for use with materials which are very heat sensitive, but it is compatible with commonly faceted natural materials such as quartz, beryl, tourmaline and garnet. Earl Zoeller, who teaches at Old Pueblo Lapidary Club and introduced me to this wax, uses it without heat related problems even for dopping opals.
For heat sources I use a Master Mechanic propane torch, the garden variety, hardware store kind that consists of a nozzle screwed onto a standard propane cylinder, and an old electric clothes iron. There are more ergonomic torches available, notably the Blazer hand torch, which burns butane and is refillable from charges for butane cigarette lighters. I pressed the propane torch into service prior to acquiring a Blazer of my own. At about $60 or so the Blazers aren't cheap, and somehow I've just never gotten around to shelling out for one. The flame and heat output on my propane torch throttle back nicely, and it works for me. I'll probably get around to acquiring a Blazer one of these days, but it seems like I almost always have some necessity of higher priority on my faceting want list.
The iron was a second hand store item that's mounted upside down on a simple wood cradle, so the heated flat surface is level and facing up.
I use the iron as a pre-heater for the rough. I have the thermostat on the iron marked where it gets just a little more than hot enough to melt the wax, but well below smoking or burning it. I bring the stone up to heat on the iron gradually in half a half dozen steps or so spread over about 15 minutes. The general idea is to not thermally shock the stone with a sudden or uneven change in temperature, so it is gradually brought up to the working temperature of the wax. Like coming to Tucson during the summer, it's not the absolute temperature per se that kills you, it's the shock... ;)
This technique for black wax involves some preparation prior to applying heat.
One pitfall is not having an adequate selection of dops. The largest available dop compatible with the (planned) finished size of the stone should be used to maximize the area and strength of the wax bond. The problem with not having the one that's 'just right' on hand is you can't use the one that's too big, so you wind up using the one that's too small.
Dops should be scrupulously clean - wax from prior projects should not remain on them, including inside the cones of cone dops. Drugstore variety isopropyl alcohol works as a solvent for the black wax and I have also used acetone and MEK depending on what was handy.
I keep a small jar filled with solvent for cleaning dops. I just open and drop in those that need cleaning, close, and let time do most of the work. Wiping with a soft rag or paper towel is usually all that's required to finish the job. An X-acto knife with a pointed blade is handy for removing any stubborn residue from inside cones or other nooks and crannies.
I find the thermal characteristics of brass are the most user friendly for dopping with the black wax. It seems to have just about right heat transfer and retention. I also use black wax successfully with steel dops. Steel heats up slower and retains heat longer, so you just need to be a little more patient and judicious with the application of heat.
If you keep the heat on steel dops continuously until the stone end gets hot enough to melt wax, there's often enough heat built up internally in the dop that even though you remove the heat source when the wax begins to melt, it continues conducting to the stone end and next thing you know you've got black wax flambeau.
I have only tried to wax dop with an aluminum dop once. I found aluminum to be difficult to use because it cools down too quickly to give you much working time for tweeking the centering of a stone or creating a wax fillet between the stone and the dop.
I sometimes wipe and dress the stone end of my dops with 320 wet-dry, which leaves a clean, fresh surface and fine scratches in the brass. Maybe superstition, but I think the fine scratches may help the wax bond. I'm sure the clean part does.
I use the transfer fixture as a clamp to hold the stone in position against the dop as things cool and the wax hardens. I usually cut pavilion first, so a temporary table is ground on the rough to serve as the plane of attachment for the crown side dop. I've always used a flat dop against flat surfaces, but I know other wax doppers who prefer to use a cone against flats on the theory that when the wax inside the cone cools it shrinks, creating a suction. There might be something to that, as the wax definitely expands when it is heated, and a good wax bond appears to be gas tight. In any event, their stones don't fall off and cones as well as flats have proven serviceable against a temporary table.
A 'cold' run is part of the preparation. The crown dop is placed in the transfer fixture which is set down on the work surface so that the flat of the crown side dop is facing up and horizontal. The fixture needs to be able to freestand on the table, leaving your hands free for manipulating the stone and torch and other tasks.
The rough is placed on the dop with temporary table upside down and in contact with the flat on the dop. This puts the pavilion side of the stone facing up. A second, small diameter dop is placed in the fixture and lowered until it contacts the pavilion side of the stone, pinning the stone between it and the the crown side dop. I use a 1/16" flat dop for the pinning dop, but one that was ground to a moderate point might work even better.
It is often necessary to cut a small flat on the pavilion side of the stone to create a level pad centered above the culet for the pinning dop to push against and exert an evenly distributed pressure. The rough is adjusted until it is centered on the crown side dop, and then I mark the contact point of the pinning dop on the pavilion side of the stone with a fine point marker. This mark makes a convenient alignment reference for when you're putting things together hot.
I have an assortment of tweezers and modified pliers that I use for picking up and manipulating stones of various sizes and shapes when they are hot. During the cold run I make sure the pair I plan to use can easily grasp and release the particular piece to move it from the iron to the dop, and to manipulate it. More and more I find myself simply picking up and moving the stone with my fingers, but there may be a bit of a Zen thing there, and your tolerance will also vary with your callous pads and the size of the stone. One thing I have learned is that it is risky to heat a stone searing hot and that it is unnecessary to do so to dop it with black wax. It doesn't need to be hotter than the working temperature of the wax.
Using the iron for a preheater helps bring some control to the process and insure excessive amounts of heat are not applied to the stone. You could also homebrew a pretty serviceable preheater from a light bulb, juice sized tin can and a dimmer switch. It's easy enough to find the appropriate setting on the iron by trial and effect with a bit of wax for testing. I might be inspired to incorporate a thermometer just for fun at some point when I run across some appropriate electronic junk, or maybe a meat thermometer.
My transfer fixture has spring loaded fingers that press the dops into a v-groove. Once positioned, I clamp down on the crown side dop so that it is immobilized. The spring pushing against the pinning dop is adjusted so that it can still be slid up and down in the v-groove with finger pressure, but with enough friction that it will hold its position and pinning force against the stone once it's slid home. When everything is correctly adjusted and the stone is properly pinned between the dops, the fixture can be gently lifted, rotated and set back down on the table inverted without the stone falling out or shifting position.
The stone and the crown side dop are given a final wipe with a rag or paper towel moistened with isopropyl alcohol or acetone to remove any skin oil or other contaminants just prior to heating things up.
I determine when the rough and dop are up to heat and at the working temperature of the wax by melting some of it on the surfaces that are going to be brought together and bonded.
If the rough won't sit on the iron by itself so as to orient the temporary table up and level, I place it on the iron using a simple fixture made from one of several metal rings fabricated from thin slices off copper and brass tubing or pipe. Several of these have notches filed into them here and there as needed to accommodate odd or irregularly shaped rough. Once level, a chip of wax is placed in the center of the temp table and the rough incrementally brought up to working heat with the iron's thermostat as previously described. When the wax on the stone begins to melt and flow out across the temp table, I fire up the torch.
A chip of wax is placed on the flat of the crown side dop, or usually I just melt off some drops from a piece with the torch, which harden as soon as they contact the still cold dop. Once sufficient wax has been transferred to the surface of the crown dop to cover it with a thin layer when molten, it is then heated indirectly by applying the heat from the torch to the body of the dop, rather than directly at the wax. If you train the heat of the torch directly on the wax for any appreciable time it goes flambeau. The object is to melt the wax without getting it so hot as to smoke and burn it. The wax melts when the dop reaches working temperature. Wax that has been overheated and burnt or fried does not bond properly.
Black wax will flow and follow a flame (heat) just like solder. When the wax on the dop melts and flows, it will readily 'wick' across and coat the entire flat of the dop provided it is reasonably level and clean. Once the dop is up to heat and the wax has reached a liquid state (with some usually running down the side of the dop and off onto your work surface), you can direct and 'tease' it into flowing where you want it with heat from the torch applied to one side of the dop or the other.
The wax will first bubble, and then boil vigorously and start to get a little smoky just before it goes flambeau. When I'm initially prepping and melting it onto the surface of a dop with indirect heat, I use the appearance of small bubbles (like simmering water) as an indicator it's time back off with the torch.
BTW, have I mentioned that it's probably not a good idea to do wax dopping over your significant other's good dining table cloth?
At this point everything is up to heat with the dop surface and temporary table both coated with a layer of wax molten to a liquid state.
The stone is picked up from the iron with tweezers or callused pinkies, inverted, and the temp table is placed down against the flat of the dop. The pinning dop is then lowered against the pavilion. As it nears contact, the centering of the stone on the crown dop is tweeked as needed so that the pinning dop is brought home on the position mark created during the preparatory cold rehearsal.
Virtually all of the still molten wax will be displaced from between the dop and the table when the stone is placed on the crown side dop and the pinning dop is brought home. As soon as clamping pressure is applied with the pinning dop and the stone is securely positioned, the transfer fixture is inverted so that the pavilion of the stone is now facing down. Displaced wax which ran down the side of the crown dop (now up) and away from the stone, now runs back down the side of the dop towards the stone.
If everything is just right and you are having a good day, a nice uniform, convex meniscus or filet of wax will form between the circumference of the crown dop and the temp table as the displaced wax flows back down to the stone. This filet is desirable to help increase the surface area and strength of the wax bond.
More often than not a properly formed filet requires a little help. If there is enough wax to make the filet, but it is unevenly distributed to one side or the other, the barer side of the crown dop can be judiciously licked and heated with the torch to lead the excess wax over from the thicker side in conjunction with tilting the transfer fixture so as to encourage migration of wax in the desired direction.
Often there is not enough wax to create a good filet, so some more is applied, either by touching a cold piece of wax against the dop to melt some on it, or by training the heat on a piece of wax to melt and drip some off onto needy areas. If there is enough wax to make the filet but the stone is still hot enough that it slumps down and spreads out across the temp table instead of forming a filet, invert the fixture again to run the wax the other way. Sometimes the fixture gets inverted and flipped over several times to direct the still molten and flowing wax up and down, so that it is manipulated with gravity into position and properly distributed to create a nice filet when it thickens as it cools and starts to harden. A smooth and nicely formed black wax fillet is a thing of beauty, as it is a pretty reliable indicator that all came together at adequate working temperature, and that you have achieved a serviceable and robust bond.
The working time that you have to go through the necessary motions and how long things stay at the working temperature of the wax is longer for larger stones and dops. With larger projects you can work at a rather leisurely and relaxed pace before things cool to the point that the wax begins to harden. If things do begin to cool down before you want them to, you can inject more calories by heating the body of the crown side dop with the torch. It helps to have the fixture oriented so that the stone is above the dop as additional heat is applied to take advantage of convection to help distribute the additional heat more uniformly.
A goal of this technique is to bring everything together and get all of the positioning done while both the stone and dop are both still slightly above or at the melting point of the wax. If the temperature of the dop or stone falls below the melting point of the wax and it begins hardening while you are still moving them around relative to each other, the wax bond is weakened and compromised. When that happens you get a 'cold' bond, somewhat analogous to a 'cold' solder joint. Similar to cold solder joints, cold bonds are prone to fail during the faceting process when they are stressed.
Once everything is together and the filet is up to snuff, the whole shebang is allowed to cool slowly to room temperature without further disturbance. It's a good idea to turn off the iron and torch as soon as you are finished with them to help prevent accidents.
The black wax gets quite hard, but not so immediately after cooling down to room temperature. There seems to be a pronounced difference in the hardness and quality of the black wax bond after a dop job has cured overnight. I think this hardening process continues further with time, as wax on stones I dopped a year or more ago seems *really* hard now.
I've never seen evidence of it through my own use, but I have heard others talk of stone shifting problems with the black wax. I assume due to softening from polishing processes which cause significant heat build up in the stone. I can see where that could be problematic for black wax, but it works very serviceably for me with the water lubricated cutting and oxide polishing processes I am using on materials like quartz, beryl, garnet and tourmaline.
After cutting and polishing the pavilion the stone is ready for dopping to the pavilion side dop and transfer.
An appropriate (largest available that fits) cone dop is secured in the transfer fixture, which is placed on the work surface so the cone is facing up. Chips of wax are placed in the cone or it is dripped in by melting a larger piece with the torch. If the pavilion is keel shaped rather than conical, molten wax can be contained by a v dop by temporarily damming its open ends with a wrap of tinfoil.
The pavilion is wiped with alcohol or acetone to remove any skin oil or contaminants, and the crown side dop is placed in the transfer fixture opposite and over the cone dop, with a gap of half an inch or so separating the culet from the cone dop. The tension is adjusted on the crown side dop so that it rests snugly in the v of the transfer fixture, but can still be slid up and down smoothly within the v.
Heat from torch is applied to the body of the cone dop until the wax within is molten to a liquid state. The black wax expands considerably when it melts and that effect is observable when you melt the wax in the cone.
It is generally not necessary to fill the cone all the way up to the lip, as most of the molten wax will be displaced when the pavilion is slid home inside the cone. The excess is used to create a filet between the circumference of the cone dop and the stone as previously described for the crown side dopping, so a filet's worth of excess volume is really all you need. More doesn't really hurt anything process wise, but you are again advised of the possible danger involved in doing this over a good dining table cloth...
When the wax in the cone dop has liquefied, the gap between it and the culet is reduced to nearly touching, and convection is used to warm the culet. After ten seconds or so warming, the culet is submerged to just below the surface of the molten wax by sliding the crown side dop down in its v groove slightly. A few more seconds for further warming, and the stone is lowered into the wax a little more. Then a few more seconds and lowered a little more, repeating until the pavilion is home in the cone. It may be necessary to lick the body of the cone dop with the torch at intervals during the process of lowering the stone into it to keep the wax liquid and at working temperature.
When the stone is home in the cone and the pavilion is sufficiently warmed, the wax 'wicks' out onto the surface of the stone at the interface with the wax bond, and a small meniscus forms. The general idea is do things at a rate which does not thermally shock the stone, but brings the pavilion to sufficient heat so that the wax bonds to it properly as you go.
Once there, the fixture is flipped over to recover wax which has run down the outside of the body of the cone dop, and this excess wax is manipulated using gravity and a little directed heat if required to reinforce the perimeter of the bond with a filet, as was previously done with the crown side dop. You can add a little more wax if need be by touching a piece to the dop and melting it on.
Everything is then allowed to cool to room temperature and the wax to harden. Now you have a stone with dops stuck to both ends. The assembly is removed from the transfer fixture, and the crown dop is removed. This is done by holding onto the pavilion side dop and orienting the assembly so that the dops are horizontal. Heat from the torch is then applied to the body of the crown side dop until the wax bond securing it to the stone softens sufficiently and the dop drops off on its own accord. The dop will be pretty hot when it falls off, so you don't want it to land on your bare foot or a surface which could be marred by it. A recycled pot pie tin can be handy here.
Remaining wax adhering to the crown side can be readily removed by scraping with a thumbnail while it is still warm. I remove most of it because I don't like to contaminate my laps with wax, and I usually need a clean girdle facet or two to re-align the stone to the lap after transfer, as I generally don't use the dop key on my Mark IV. I learned to remove the remaining wax from the crown with my fingernail while it is warm, instead of scraping it off with a knife after it has cooled and hardened. I once caught the edge of a temp table while doing that, and cleaved off a sizable chunk that went right down through the girdle, ruining all my work. I won't be doing that again.
Once the crown has been faceted and finished, it only remains to part the pavilion side dop from the stone and clean it.
The dop is clamped in the transfer fixture, which is used as a handle as heat from the torch is applied to the body of the dop. The transfer fixture is held so that when the dop reaches the melting point of the wax, the stone is free to part company and fall away. Of course you do this just above a soft surface that has been prepared to catch the stone when it falls. I simply use a soft rag to catch the stone when it parts company with the dop. Once off the dop, a brief soaking submerged in a small container of isopropyl alcohol or acetone softens and dissolves the remaining wax, and the stone is wiped clean with a paper towel or soft rag.
I have never tried using shellac as a bonding agent with the black wax. When the surfaces to be bonded are clean and up to proper working temperature, the black wax readily 'wicks' and clings to them. I have experimented some with a preparatory wash made from wax dissolved in alcohol or acetone, applied to the stone as a primer when cold. However, the end result and quality of the bond seems the same with or without this preparation.
In my experience, bringing the parts to be joined to the proper temperature (a little above melting point of the wax) and maintaining that working heat during manipulation is the most critical aspect of getting good bonds with the black wax. With a melting point of about 165 degrees F, that can be accomplished at very reasonable stone temperatures with black wax as soon as you've practiced a little with heat control.
Using the technique I've described, the heat from the torch is applied to the stone indirectly by heating the dop and not the stone directly. I don't find it at all difficult to control and modulate the heat from propane or butane torches, and I prefer working with 'hot' and concentrated sources like that instead of alcohol lamps, which are frequently associated with and used for wax dopping.
As mentioned earlier, I've found even a hardware store variety propane torch like the kind that's used for sweat soldering copper plumbing joints to be serviceable. It's not so much a matter of the size of the torch as the ability to adjust and control the flame and heat, and a little practice with it that's important.
While I've run on describing the process I use with black wax in detail, dopping with it is one of those things that's more readily done than described. You'll often hear wax dopping described as an art and something that's difficult to do. That simply hasn't been my experience with this wax. If it were of that nature I would be using some other wax or general dopping technique.
I have only once had a black waxed stone break loose from the dop. That happened early on, on my third stone, which was first one I dopped on own at home without the supervision of the instructor who introduced me to black wax. I had a cold joint and found out about it as soon as I started roughing out the stone.
There are a number other dopping waxes available and used by faceters on gemstones, one of which is a brown wax which seems to be preferred by a number of other faceters I know through Tucson's Old Pueblo Lapidary Club. That wax has a higher melting point than the black wax, and the specific techniques I have observed other faceters employ for dopping with brown wax vary significantly from those I've described for black wax. In general, I see them using it in a more viscous and plastic, rather than liquefied state. Some of them tell me they particularly prefer the brown wax for dopping smaller stones, and also for polishing hard stones like sapphires with diamond, where a fair amount of heat can be generated and transferred to the stone.
I tend to work on the larger side with materials like quartz, garnet, beryl and tourmaline which I cut and polish using water lubricated processes. I have found black wax to be easy to use and very serviceable and reliable for them. Black wax works for me.
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