This accomplishes several things:
1: It adheres the diamond particles to the lap.
2: The oils provide lubrication to lessen overheating of the stone being cut.
3: The cooling water is still free to remove the swarf or dust from the cutting. Most of the "colored" stones we cut are hydrophilic..Usually they are silicates or other compounds which "like" water.
A couple of suggestions and observations were advanced on the Faceters' Digest regarding the use of oxide polishes in nonpolar (Oily) bases. Results on tin alloy laps ranged from encouraging to astounding. Traditionally, these polishes were not compounded into nonpolar bases...without proper surface treatment, or milling such as is used in the pigment industry, they did not produce good dispersions.
But there is a way.
By coating the polish particles with a polymeric dispersant, we can reverse the apparant polarity of the particle and force them to behave as diamond does in oily carriers.
Such a dispersant has a hydrophile end which bonds to sites at the surface of the particle, and an oily "end"consisting of a chain of 20+ carbon atoms which sticks out into the oily carrier. The carrier "thinks" the particle is a lyophile. This mechanism is called "Steric Stabilization"
This results in lubricious, cool-running polishes which last on the lap, produce fast competition-grade polishes, allow good swarf removal for less lap loading, and does so at a lower price than that of diamond compounds.
The preparation of these polishes involves some interesting applications of colloid and physical chemistry. First, there is an optimum concentration of polish for each type of oxide and each particle size range, and an optimum amount of dispersant. The nominal particle sizes vary considerably in these different materials, and therefore the surface area per gram is different. So the different oxides require a specific amount of dispersant to properly coat them.
Additionally, great care must be used to prevent the formation of agglomerates. These "clumps" can fool the dispersant, and they can mimic larger, scratch-forming particles..As we all know, this is a disaster, because usually these particle wait till we are finishing the table of the stone!
The solution is simple, if a 200 Watt ultrasonic disperser is used.
Originally, diamond abrasive compounds were mixed with simple animal or vegetable oils and fats. Olive and peanut oils are still used in diamond cutting, and even some modern diamond compound formulators are using materials as simple as "Crisco" vegetable shortening. Diamond is lyophilic, or "Oil loving". It has such an affinity for oils that greased belts running in a stream of water can be used to seperate diamond from silicate gravel (which is hydrophilic).
But what if the polish we choose is not diamond? The oxides of cerium, tin, zirconium, titanium, chromium, and aluminum all are capable of producing award-winning polishes. But these compounds are hydrophiles, and are usually supplied in water suspensions. Sometimes the suspensions are only stable at certain pH ranges, and these values may not be appropriate for the stones being cut, or the metals used in the construction of the machine or the lap. Being in a water base, of course, there is little to keep them on the lap if cooling water is used...And some of them are chemically identical to the stones we cut. Control of rheology:
Ideally, the polish should be a stable solid in the container so particles do not settle or agglomerate. When applied to the lap, the polish should liquify immediately and flow to a uniform film, but then stay in place on the lap. Here is some compound made with cerium oxide. It is a free-flowing liquid as it passes through the syringe nozzle, but immediately gels when the flow velocity drops.
Results have been encouraging enough so that I can now release them. A trial set of the cerium oxide formulation and the aluminum oxide formulation in 5CC syringes can be ordered for $10.00 postpaid.
Send Check or Money Order to:
PO Box 533
North Easton, MA 02356 USA.
