by Jeff Ford
The following article describes a hybrid method of dopping with a combination of wax and Cyanoacrylate Adhesives, aka “Super Glue. Note the acronym “CA”, will be used throughout this text to describe Cyanoacrylate products, adhesives, and glues.
I first learned of this method via several post on the USFG faceterslist. Art Kavan and Dieter Irmischer were discussing methods of dopping they use for competition cutting, later I learned that they use this for the majority of stones they cut. Both Art and Dieter deny coming up with the original idea, but Dieter does credit Charles Covill with it by the way of information presented at a faceters symposium hosted by the OPLC several years ago. Along parallel line of thinking, list member Oya Borahan from Turkey has described a similar method of hybrid wax/glue dopping she has developed independently.
We will be exploiting the fact that CA glue will bond quite well to both dopping wax and polished gem surfaces, the technique involves both the use of quality dopping wax (Leco or Black) and CA style glues. This presentation will be broken down into two parts addressing the crown and pavilion dops separately. The goal of this technique is to first coat the dops with a thin layer of dopping wax that matches the exact profile of the gem, then attach the stone with a small amount of CA glue.
About CA’s – Part of the research for this article involved a telephone conversation with Mr. Bob Smith, of BSI Inc. of Atascadero, California. (www.bsiadhesives.com). BSI is a sizable manufacture of both CA and Epoxy products catering to the private label retail hobby industry. Mr. Smith states that in general, CA products will provide stronger ultimate tensile bonds vs epoxies. This is based upon the fact that in practice it is difficult to achieve the perfect “mix and ratio” with epoxies using the resources available to the normal end user. Normally epoxies are quite forgiving and will tolerate a +/- 10% variance in ratio. But do not be lulled into the belief that altering the ratio any further will somehow produce results of increased hardness or flexibility. Another problem with Epoxy product may be entrapped air (in the form of bubbles) as a result of the mixing process.
Cured CA is actually acrylic plastic. CA’s cure or polymerize when pressed into a thin film in the presence of a slightly alkali environment. In general, ambient humidity in the air and/or on the bonding surface will provide the proper pH to initiate cure in a few seconds. The best bonds are achieved when relative humidity is 40% to 60% at room temperature. If the surfaces to be bonded are excessively dry or are acidic, the curing can be much slower or not happen at all. Most manufactures will agree that depending upon humidity, CA’s may take as long as 24 hours to achieve full cure. As a point of interest, gel and thickened CA’s are produced with additional components to induce various levels of thixotropic or gel qualities.
Still on the topic of CA, Mr. Smith goes on to say that for the strongest joint possible, unless the application warrants the use of an curing accelerator (or kicker), accelerator use should be avoided as they will generally provide reduced bond strength vs using straight CA alone. Remember that CA’s work best with very thin, well mating joints! Dealing with thick or irregular joints is often the reason why accelerators are used, i.e., to compensate for variations from the ideal width, which is typically around 0.1 to 0.3 mm in width. Again just keep in mind that tight joints are best, hence only use enough CA to fill the joint, i.e., excess CA should not “ooze” out of the joint. If this happens you have way too much! Excessive amounts of CA will only retard the cure and in some cases may result in only a partial, or even worse, no-cure at all.
For the record Mr. Kavan, Irmischer, and Covill all promote the use of “Zap-a-Gap” (www.zapglue.com) as a reliable product they have all used very successfully.
Not to totally discredit epoxies, because they do several things very well. 1), since they are a catalyzed or cured polymer product, they will fully cure through very thick or irregular sections. CA products will not do this with joints over the recommended thickness! 2), in general the epoxy joints are very tough, that is to say that they will tolerate a great deal of abuse and shock. 3), the cure times may be controlled with the use of catalyst (provided by the manufacturer), in general though one may state “the faster the cure, the weaker the bond”. 4), epoxies may also be post cured (or accelerated) with the addition of heat.
Just a few quick words about using wax and safety – Some faceters do claim that wax may be recycled. Honestly for the price of “new” wax and to avoid any possibilities of contamination. It is my personal opinion to never do this, it’s just not worth a few pennies to salvage used wax. Along the same lines the use of dopping wax does involve fire, hot liquefied wax, and flammable solvents. With fire, please be safe about keeping the area free of loose combustibles, solvents, etc.
Jigs – The jig I use was purchased as a Graves “Deluxe” model. Comparing photos with other cutters it looks identical to the jigs offered by Polymetric. One end of the jig is fixed the other clamps and/or slides along the length of a round rod. The clamping mechanism is basically a form of a dovetail slide. In addition, I use a bench mounted Pana-Vise to hold the transfer jig in a vertical orientation, or any other position I choose for that manner. For the fire source I use one of the small refillable hand held butane models with a pizo electric spark igniter.
The crown dop is first prepared in the following manner – Note both dops are cool, clean, and ready to go. The first course of business it to align the flat on the crown dop. To do this two flat dops are used, I will refer to them separately as the hot dop and the cold dop. The hot dop will be the one used for ultimately holding the stone. The size of it will be up to the cutter, and will not be covered here. The cold dop will be the next size up (or even larger) and it is placed in the movable end of the jig.
Just a quick side note about the cold dop: It should be totally flat (no groves in the surface) and perfectly square to the axis of the dop. Some cutters may use an oversized target dop for this. If needed a spare dop may be machined square and perfectly flat.
The hot dop is next placed in the fixed or lower portion of the jig. Both dops are cool, cleaned, clamped, and ready to go. The hot dop is gently heated and a puddle of wax formed on the flat face. The wax is allowed to cool just to (or just past) the point of solidification. This may be tested with a clean toothpick. It is important that the wax should somewhat solid, but still be pliable. Sort of like butter at room temperature. Next the cold dop is lowered then pushed on to the warm wax for several seconds then removed, or raised as in my case.
The goal here is to end up a thin flat, coating of wax on the dop you will be using for the crown of your stone. In practice this coating will be somewhere between 2 to 3 mm. The cold dop accomplishes two things for us; 1), it flattens out the puddle square to the dop axis of the jig. 2), the cold dop will accelerate the “final or hard” solidification of the wax. Since the dop is cold, nine times out of ten, will not stick to the wax when it is removed. This is where a little practice pays off. You’re done after the hot dop returns to room temperature. Important do not touch the new wax flat, we do not wish to contaminate it with skin oils or any contaminate of a similar nature.
Next the stone is attached to the crown dop. The stone should have a flat produced with something like a 600 grit flat lap. In reality when using CA adhesives smoother is better, but more importantly it must be flat vs curved or irregular. Now clean the stone in your choice of solvent, remove any oils or foreign matter. Note I have heard reports (from Bob Smith and others) that the use of acetone may indeed leave possible residues left after evaporation, that may be counter productive with respect of preparing surfaces for ideal CA bonding. On the safe side, any of the alcohol solvents would be the preferred choice for cleaning. The CA of choice will be a quality, medium thickened glue, but not necessarily the gel variety. It is important to use “just enough” CA glue to just squeeze out to the joint. As too much will generally slow the curing process. For small (6mm) stones, a very small amount is needed. For example a sewing pin may be used to apply small amounts of CA by first dipping the end in a drop of glue. For larger (20 mm) stones the total amount of glue will be about half the size of a BB. The CA glue is placed on the wax surface of the dop only, preferably is several small spots vs a single blob. Next the flat of the stone is positioned and brought together with the dop. Once contact is made press and hold the stone to the dop until the CA grabs tight. With a little luck the stone should be initially set in a matter of seconds. My personal habit is to wait at least one half hour before attempting any cutting, but overnight is always a safe bet. Now go have fun, cut the pavilion on your stone!
The preparation of the pavilion dop – The pavilion dop is prepared in a manner similar to that of the crown dop. With the major exception that the cut pavilion of your stone will be used instead of the cold dop to form an exact impression (or negative replica) in the warm dop. With a little practice Vee dops may be prepared in a similar manner, but it will not be covered in this text.
Clean the pavilion surface (of the stone on the dop) with fresh alcohol and clamp it in the upper (movable) clamp of the transfer jig. A clean cone dop is clamped in the fixed end of the transfer jig, with the dop vertically orientated, cup up.
The cone dop is next warmed and filled with a pool of molten wax. Please note the goal here is not to overcook, boil, smoke, or burn the wax, we just wish to gently liquefy if it. Most cutters will agree that over heating the wax will result in an inferior joint. Next the wax is again allowed to cool just to the point of solidification. Remember the analogy to butter? Again use a clean tooth pick to test the consistency of the hot wax.
The upper stone in next pushed/plunged vertically down into the pool of wax. Continue to push the stone into the wax, but pull up short of bottoming the stone out! We don’t want the culet to touch metal when we are done. If properly done bottoming out will not be a problem, as the cool stone will accelerate the hardening/thickening of the wax.
After a count of two or three pull the upper stone back up, clear of the lower (cone) dop. I have found if the upper stone is left down much longer sticking may result. Note at this point both dops are clamped, but the dop with the stone is allowed to travel freely along the dovetail of the jig. If you find that the wax has not quite adequately solidified, the cold end may be used again to touch up the wax impression. Just keep in mind that we are looking to end up with the 2 to 3 mm wax thickness and not have the stone touching any bare metal.
Since the wax is fairly warm, and the stone is relatively cool, the wax with any degree of luck will not adhere to the stone! The result will be that a perfect impression of the pavilion will be formed of the pavilion in the lower dop. It is important at this point not to touch the wax cup to insure the best bond possible. It is best to just set the assembly to the side until the pavilion dop has cooled to room temperature. Next apply a small amount of CA glue to the cup and lower the stone to spread the CA. Both dops should be firmly clamped at this point. Allow the assembly to set for one half hour minimum, again waiting over night is best, before proceeding to the next step.
Now here is the beauty (or perhaps genius) of this method: To remove the crown dop simply hold the assembly in the horizontal position. Next, apply just enough heat to the crown dop (heating the metal portion of the dop only!) until the dop simply falls or slides off. Making sure the stone is at room temperature; remove any excess wax and CA glue with a hobby knife and a little acetone if needed. With some practice others may choose bring the temperature of the metal dop to the point where the dop may be twisted off with the lightest pressure.
Now go ahead and cut the crown! – Now we are ready for the best part! Removing the stone from the pavilion dop is very simple. One of two methods may be used; 1), the cutter may again gently heat the metal portion of the dop and allow the stone to be removed with a light twist and/or pull. 2), the stone may be separated from the dop with a good overnight soak in denatured alcohol. In both cases the stone will require soaking in alcohol to remove any remaining wax. Removing the remnants of the CA bond is simply accomplished with an additional soak in acetone.
General advantages of this method – If for some reason the stone should ever become separated from the mating dop, it may be easily re-attached with a little CA glue to the perfectly mating dop! Often any wax or adhesive stuck to either the stone or dop will act as a “key” to reposition the stone in practically the exact position prior to the separation.
Shifting during transfer due to over heating the stone is eliminated. Wax by it’s self alone also has a disadvantage of shrinking as it cools. Normally this is not an issue, but it may also explain some problems that cutters may experience from time to time with wax alone.
By using the wax barrier between the stone and dop potential chipping of the cutlet is greatly reduced. If you have any great concerns about chipping, an Exacto style hobby knife may be used to remove a small amount of wax in the culet area, do this prior to the application of the CA glue.
Cured CA is easily removed with acetone. Although acetone is not a totally benign material, it is much safer, from a health and safety stand point, than products containing methylene chloride, a suspected carcinogen, often recommended for dissolving epoxy bonds.
Some cutters comment about CA adhesives having degradation problems in water. In general faceters using CA’s will not have any significant issues considering the actual amount of limited water contact that a bond will normally see. If we were talking about total immersion of a CA joint for extended periods of time, then there may be an argument. But not here today with any of the cutting styles I have ever seen or heard about. If this is truly a concern to the cutter, the CA joint may be adequately protected with a simple coating of finger nail polish. The nail polish will later dissolve quite easily with acetone.
Compared to using epoxies alone this hybrid method is very fast. Many of the positioning problems associated with curing epoxy are eliminated.
Removing stone could not be simpler, a little heat or overnight soak in alcohol is all that is needed CA’s do have a limited shelf life. Generally they will thicken and loose potential bond strength with age. To extend the shelf life, CA manufactures often recommend storing them in the freezer. If you do this, be sure to allow them to completely return to room temperature before using.
Initially I started out dopping with nothing but black wax. Other than a few shifting problems it worked flawlessly. But after practicing this technique half a dozen times on a few old preforms I was hooked and now use it for the majority of my stones.
Although we are using wax, very little heat is directly applied to the stone itself. Okay, it’s not a totally cold dopping method, but it does come very close.
Admittedly the technique is not 100% cold and perhaps should not be used on materials that are extremely sensitive to heat. The cutter needs to be the judge here. Although we are using hot wax very little heat is directly applied to the stone itself. Okay, it’s not a totally cold dopping method, but it does come very close.
Honestly, I will be the first to admit that this method requires a little bit of practice to master. So before you attempt to mount anything of great value, take the time to practice on a few old cut stones or basic preforms.
In retrospect this method may be extended to the idea of using a double pavilion or two cone dops when cutting gems without flat tables, or pieces of valuable rough where you may not have the luxury of starting with a temporary table. Just let your imagination explore the possibilities.
At first I did not understand why Art and Dieter used this two step approach to dopping, after all it seems like more work, right? Yes, it is a little more work, but not as much as you think once you master the basic technique. Yet it retains the simplicity of separating the wax bond with a little heat or alcohol. While at the same time offering a nearly cold dopping technique. As an added bonus many of the shifting or bonding problems often attributed with hot wax alone are virtually eliminated.
Jeff Ford – 2003