FINAL RESULTS OF 3 SETTING METHODS IN STRENGTH ORDER:

• 1st Place: Conical cap adhered to externally air-abraded briolette with epoxy adhesives.
• 2nd Place: Pin-cap adhered in vertically drilled "blind" hole with epoxy adhesives. **
• 3rd Place: Cross drilled briolette using a through wire setting method, no adhesives.

**We recommend using the vertically drilled briolette-epoxy-pin-cap for smaller briolettes & the conical cap-epoxy-external air-abrasion method for larger briolettes.**

Read on to see how these results were obtained, and the advantages and disadvantages of each method.

In an attempt to understand and quantify the strengths of various briolette setting procedures I performed some basic tests. The tests subjected briolettes set according to the 3 methods outlined in the "Setting Techniques" section to an increasing weight load. The load was increased until setting failure occurred.

PROCEDURE

Six briolettes were set, two for each of the following three methods:

1. Two briolettes were vertically drilled with "blind" holes using Stuller (item #29) pin-caps adhered with epoxy adhesive.
2. Two briolettes were set with conical caps, epoxy adhesive and air-abrasion to the exterior surface of the briolettes.
3. Two briolettes were cross drilled and a wire was inserted through the holes for a setting using no adhesive.

The set briolettes were suspended and a load was applied to each particular setting method. This was accomplished by attaching the setting to a stationary beam with steel wire. The body of the briolette was carefully wrapped above it's widest point with thin steel wire. This wire was attached to a bucket into which a measured amount of weight was added until setting failure was reached. Either sand or water were used as weight in the test procedure. Results were noted.

ACTUAL TESTS (all tests performed at 60 degrees Fahrenheit on natural quartz briolettes)

TEST 1: "Thin" wire 14 kt gold pin-cap adhered w/epoxy into a vertically drilled briolette.

• briolette material & type: Russian rock crystal, rnd. cross section, 30 degree top angle, ultrasonically drilled with a 0.020" stainless steel hypodermic tube (hole diameter ends up larger than drill tube size, about 0.023")
• setting method: Stuller pin-cap, 14 kt gold, pin wire diameter reduced to 0.023" (standard dia. 0.030"),pin depth 0.085", "face"cap diameter 0.060"
• adhesive: Devcon 2-Ton Epoxy, 30 minute work time, 2500 lb./sq.in. rated, waterproof, product code "S-31" purchased at Home Depot for about $3 for hardener and resin.
• cure time allowed: 36 hours (Manufacturer says only 8 hours necessary for full strength.)
• RESULTS: Failure occurred with 8,635 grams (19+ lb.) of load. Upon close inspection there was a material failure of the rock crystal itself. The pin did not merely pull out of the hole, but broke the rock crystal along with it. The rock crystal wall along one side of the hole broke off when the pin pulled out.

TEST 2: "Thick" wire 14 kt gold pin-cap adhered w/epoxy into a vertically drilled briolette.

• briolette material & type: Russian rock crystal, rnd. cross section, 25 degree top angle, ultrasonically drilled with a 0.025" stainless hypodermic tube ( hole diameter ends up larger, about 0.030")
• setting method: Stuller pin-cap, 14kt gold, pin wire diameter left standard 0.030", pin depth 0.10", "face" cap diameter 0.075"
• adhesive: Devcon 2-Ton Epoxy, 30 min. work time, 2500 lb./sq.in. rated, waterproof, product code "S-31" purchased at Home Depot for about $3
• cure time: 36 hours (Manufacturer says only 8 hours necessary for full strength.)
• special note: Prior to testing, a small feather/finger print type inclusion was noted intersecting the drill hole upon 60x observation of the set briolette. This inclusion appeared to be natural and an inherent part of the briolette prior to drilling.
• RESULTS: Failure occurred at 5,214 grams (11.5 lbs.) of load. Upon close inspection there was failure of the rock crystal itself. Not only did the pin pull out, but it took half of the wall along the hole with it. The lower weight failure than test 1 was a surprise. Possibly due to material weakness.

TEST 3:  60 degree conical silver cap adhered w/epoxy to air-abraded briolette.

• briolette material & type: Brazilian golden citrine, rnd. cross section, 60 degree top angle
• setting method: Top portion of the briolette was air-abraded using #180 grit Aluminum Oxide (adhered conical portion of the briolette under the cap measured 0.160" diameter at the cap mouth and terminated 0.076" deep into the cap) The 60 degree sterling silver cap (our widest), corresponded to this briolette's top angle. Cap depth was trimmed to proper size in relation to the briolette.
• adhesive: 3M DP 100 clear epoxy, 3-5 minute work time, 2500 lb./sq.in. rated, purchased from 3M Distributor
• cure time: 8 months + (Manufacturer says only 24 hours necessary until full strength.)
• RESULTS: Failure occurred at 36 lbs. (16,344 grs.) of load. In this case close inspection showed very little rock was broken upon failure. Most likely the wide 60 degree angle of this briolette allowed the stresses to be distributed through a wider angle resulting in no material failure only an adhesive failure at 36 pounds!

TEST 4:  30 degree conical silver cap adhered w/epoxy to air-abraded briolette

• briolette material & type: Russian rock crystal, rnd. cross section, 30 degree top angle
• setting method: Same as test 3 with the following measurements; adhered conical portion of the briolette under the cap measured 0.135"diameter at the cap mouth and terminated 0.160" deep into the cap. The 30 degree sterling silver cap was trimmed to the proper size in relation to this briolette.
• adhesive: same as test 3
• cure time: 8 months + ( Manufacturer says only 24 hours necessary until full strength.)
• RESULTS: Failure occurred at 24 lbs. (10,896 grs.) of load. The entire briolette sheared off at the cap opening, leaving the complete adhered section remaining in the cap. Complete briolette material failure. Adhesive did not fail. The adhesive was stronger than the rock crystal.

TEST 5: Cross drilled briolette with through wire type setting.

• briolette material & type: Russian rock crystal, rnd.cross section, 35 degree top angle, briolette total length 0.62"
• setting method: The briolette was cross drilled with a 0.028" diameter hole. Through this hole a 0.022" wire was run. This wire was bent at right angles and the briolette-wire assembly was hung on the stationary beam. The 0.028" cross drilled hole was located 0.10" below the top of the briolette at a point where the briolette measured 0.10" in diameter.
• adhesive: none
• RESULTS: Failure occurred at 8 lbs. (3,632 grs.) of load. The entire portion of the briolette above the hole sheared off and broke into small pieces. The shear plane was parallel and even with the cross drilled hole. In other words the break occurred directly through the hole. This type of setting relies totally on the material strength of the briolette since no adhesives are involved.

TEST 6: Cross drilled briolette

• briolette material & type: Russian rock crystal, rnd.cross section, 35 degree top angle, briolette total length 0.71"
• setting method: Briolette was cross drilled with a .023" diameter hole. Through this hole a 0.022" wire was run. This wire was bent at right angles and the briolette-wire assembly was hung on the stationary beam. The 0.023" cross drilled hole was located 0.18" below the top of the briolette at a point where the measured 0.165" in diameter.
  
• adhesives: none
  
• RESULTS: Failure occurred at 14 lbs. (6,356 grs.) of load. Again the entire top portion of the briolette sheared of at the hole similar to test 5. This briolette withstood 1.75 times more load than the test 5 briolette. This was most likely due to the lower hole placement through a thicker portion of the briolette.

TEST SUMMARY:

The preceding six tests have demonstrated the strengths of the three briolette setting methods we recommend. The strength of the epoxy bond when properly prepared was often stronger than the briolette material (quartz) being bonded. All the tests were performed on quartz briolettes. Quartz is not the weakest of materials. Thus it could be assumed that some of the weaker materials such as apatite or opal may fail at lesser loads.

Tests 1 & 2 were performed on vertically drilled briolettes. I specifically tested "thin" 0.023" & "thick" 0.030" adhered wire pins. (These are the 2 hole sizes I most often drill with the ultrasonic. Small briolettes receive the less noticeable small diameter hole and larger briolettes receive the larger hole diameter.) Tests 1 & 2 both proved the high holding strength of these diminutive setting methods. A short, small diameter adhered pin withstood loads of 11 and 19 pounds. Well in excess of anything that will be found in ordinary usage. It was seen that the briolette material failed before either the pin or adhesive. This method of briolette setting has proven to be very strong while the small size pin-cap remains barely visible in the finished piece.

Tests 3 & 4 were performed on briolettes set with conical caps using external air-abrasion of the briolette for increased adhesion with epoxy. It should be noted that this method yielded the strongest results.The jeweler that requires a conical cap for his or her pieces can rest assured that this is the strongest method. The high load tolerance was due to the largest bonded surface area and the minimal disruption of the briolette's structure since no holes were drilled. When using external air-abrasion, our accurately made caps and proper adhesive techniques, similar results can be expected.

Tests 5 & 6 were performed on cross drilled briolettes with a "through wire" type setting. (This is the most common way diamond briolettes are set.) This method yielded only satisfactory results. It proved to be the weakest of all the methods tested, but still had a large safety margin when considering normal briolette jewelry usage. If glue is a dirty word in your vocabulary this would be the method for you. It is the traditional method of briolette setting dating back to a time when adhesives were made from horses. The main flaw with cross drilling is; the hole going through the thin end of the briolette. This hole which is subjected to the stresses of use, weakens the briolette in the area it most needs strength. Another problem with cross drilling is the fact that the load is applied at right angles to the hole. The briolette is pulled apart in a plane passing through the hole. It seems also that the wire concentrates the force at the entrances to the hole causing stress to develop. This stress may cause hole chipping or total failure.

Special Note: It would be interesting to see how the strength of these briolette setting methods compare to other more traditional ways in which stones are set. Do you think a prong set stone could stand having a wire wrapped behind it and be subjected to similar loads as in these tests? At what amount of "back" pressure would a bezel set stone break free of it's setting? Inevitably failure would occur. The question is: At what load? No setting is permanent. They are all subject to failure in one manner or another. The adhesive junction and cross drilling methods also have their limits, which I have attempted to show. These tests have demonstrated that a set briolette is strong and unlikely to fail when set correctly. (Like any delicate item care should be taken when handling them over hard unyielding surfaces like tile or concrete. A fall on this type of surface can damage anything.)

CONCLUSIONS:
In only one case did the adhesive fail prior to the failure of the briolette material. In this case (test #3) it took a phenomenal 36 pounds of load concentrated on the 60 degree conical cap/briolette assembly to cause an adhesive failure. This high strength cap/briolette junction was accomplished with an extremely small bonded area. (The conical bonded surface area of the briolette measured 0.16 inches in diameter by 0.076 inches in length!)

All of the tests 1 through 6 required substantially more weight to cause failure than a set briolette would encounter during normal jewelry use. The safety margin of strength is at least 8 : 1 and maybe as high as 36 : 1 if 1 pound is used as the maximum hypothetical load a set briolette would ever receive. (Personally I doubt that even a 1 pound load would be reached on an earring, maybe a pendant.)

The traditional method of cross drilling briolettes showed it's inherent drawbacks in these tests. Due to the weakening effect of the hole placement, this method faired the worst in terms of strength. Not only did it fail at the lowest loads (8 & 14 lbs.) but the holes were prone to chipping under even lighter loads.

In conclusion the conical cap used in conjunction with external air-abrasion and epoxy adhesives gave tremendous holding strength. This is by far the strongest method for jewelers who like the cap "look". This method is also the best for setting very thin briolettes which do not have the material necessary to accommodate a drill hole and retain their strength.

I was impressed by the strength of the small bonded pin-caps. Although not the strongest method there are many advantages to this method. It can be done cheaply without the need for a variety of different angle caps, one pin-cap can be adjusted to fit all vertically drilled briolettes, it allows the maximum amount of the briolette to show, money is saved by using less precious metal, and strength is still far beyond minimal requirements. These small pin-caps could support 11 and 19 pound buckets filled with sand before letting go. And even after they let go it was not the adhesive that failed as one would expect, but the stone itself that broke under the strain.

The big surprise was how little load the cross drilled briolettes could handle. Cross drilled briolettes faired the worst in these tests. Although this method is capable of handling normal use loads, the margin of safety is less. There may also be some chipping problems with this method where the wire enters and exits the hole through the briolette. (Strength of this method can be increased by cross drilling the briolette at a wider diameter, lower position. This however becomes unsightly and impractical.) The one big "plus" of this method is the lack of adhesive use. For jewelers to whom adhesive is a bad word, this is your method.

These tests should have clarified most of the uncertainties jewelers have had when setting briolettes. The strengths demonstrated by each of the 3 setting methods should allow for educated decisions on the part of the jeweler. Decisions made with information gathered from these tests will have the certainty and knowledge of the advantages and disadvantages of each setting method. Any of these 3 methods will yield good results. When using adhesives and proper techniques one should not fear that the briolette will fall out, or come "unglued". To the contrary, evidence has shown that the set briolette can withstand major forces placed on it while remaining unharmed. If the briolette was to get caught and receive a good strong tug, the user would be well advised to have a personal injury insurance policy, since it will probably hurt the user more than the briolette.

And the winners are.........(drum roll please).............vertical drilling using the pin-cap & epoxy method for small briolettes, and the conical cap & epoxy with external air-abrasion for larger briolettes.

Steve Green
Rough and Ready Gems, Inc.