CERIUM OXIDE and its relative, Barnesite, are now largely doing the work formerly done by rouge in the precision optical industry, though it is not likely that rouge will ever be abandoned. The new materials are used mainly like rouge but there are some minor differences in working technique. One reader of this department, Jacques Labrecque, 560 Dunlop Ave., Montreal 8, P.Q. Canada, writes: "I have hit a problem. Every time I try cerium oxide it slowly regrinds my mirror. What is the cause of this?"

This inquiry was referred to Fred B. Ferson, Ferson Optical Co., Biloxi, Miss., who has used much rouge, cerium oxide, and Barnesite, and who offered the following suggestions: "Maybe this worker has been putting too much cerium oxide on his lap with too little water and this use of too dense a suspension has caused the cerium to roll and enamel the glass. This happens when there is too much cerium oxide (or, for that matter, any other polishing agent) either to become embedded in the lap or pushed off from it. The enameled surface then has the appearance of a very fine, iridescent grind, the iridescence being caused by interference of light reflected from layers of different thicknesses. An enameled spot on a mirror or lens is clearly visible in the Foucault test, both in outline and thickness. The enamel is on the glass, not of it, and is only of the order of one wavelength in depth."

Cerium oxide is more likely to enamel than rouge, but not if properly used. Therefore, the question of how much water and how much polishing material to use on a pitch lap may be treated as a single, general question of basic interest and usefulness to all glass pushers, amateur or other.

As Everest has pointed out in "A.T.MA.," if too much rouge is applied to a lap the mirror gets a long, free ride but not much polish. Many beginners and not a few others slap on rouge much as a green mechanic squirts oil on and all over a bearing: if a little is good, he thinks, a lot must be better. However, it really is difficult to believe that a very little polishing material can do the work it actually accomplishes.

Regarding the amounts of water to use in polishing there are two parties, the Wets and the Drys and, between them, a third party, the Moists. "On way to polish," Ferson points out in describing the Wets, "is to use considerable water, weight the lap (I refer to machine system using sub-diameter polisher, lap on top), and accomplish the polishing by means of the weighting. The opposite is to use a minimum of water and permit natural drag to take place, as it will do whether the work is weighted or not. This develops squeals and some lens shops sound like a penful of pigs. The main disadvantage of this Dry method is probable overheating of the surface, so that this method is not suitable for fine figuring, and another is the likelihood of producing sleeks (hairline scratches). These effects can, of course, be quickly adjusted at the end of the run by applying more water and continuing polishing a few minutes.

"In production work," Ferson continues, "where many jobs are in progress at one time, one man can give attention to more laps where the wet method is used, since the dry method calls for addition of water and polishing agent drop by drop. Once, in watching work in a spectacle-making shop, I saw the operator standing with a pail of rouge and a huge brush with which, after dipping it in the pail, he would flip rouge on the many spindles without moving from the spot-of course with great loss of rouge and the whole place painted red.

"The enameling mentioned by the inquirer may also occur when the lap is not quite in contact at some point."

Standing between the Wets and the Drys are the Moists. Your scribe once helped Dave Broadhead, Wellsville, N. Y., a Moist, by doing the heavy looking on while he parabolized two 10" rnirrors face up using a 5" lap on a modified Draper machine with Barnesite as the abrasive. Having made several thousands of roof prisms in wartime, Broadhead must have learned a few things optical, so his methods may be worth studying.

He put a spoonful of Barnesite in a drinking glass of water.

With a fine artist's brush having only a few hairs he stirred this up.

Then he shook the brush a little in the top of the still roily water to shake out possible grit.

Next he brushed a little of this mixture on the lap, which was a new one just made, and this was to be the total polishing material used for the one or two hours of figuring spells.

He washed the mirror and set it on the machine, then washed his hands with soap, to avoid possible grit.

Using his dried hands as a towel, he rubbed off nearly all the water adhering to the mirror, placed the lap on it, and started the machine.

Soon a tendency to squeal developed; he was working as a Moist. He worked throughout as a Moist, not a Wet. He sat beside the machine like a nurse at a bedside and, each time the pig showed first signs of squealing, he dabbed on a tiny droplet of water from the top of the now well-settled water in the tumbler.

Here was a constantly maintained nice balance between squeal and notsqueal-diligently keeping in Moist territory all the time. To accomplish this the little droplets were added about once in 10 or 15 seconds on either side of the moving sub-diameter lap. If you fall asleep at it the pig wakes you up.

Maybe faster ways could have been found to parabolize. But isn't it better to find ways to stretch out the action? You are not so likely to barge into a bad situation and aggravate it before discovering what you have done. Case of feeling your way and remaining always in full control. What's an hour or two for parabolizing a 10" mirror?

The lap backing was the stiffest possible, made of 5/16" steel plate with welded radial ribs and driven by a central pin having a bulbous head exerting its sidewise force deep in a hole near the working level. It also was light-pound or two. Since the driving pin rode free in a vertical hole in the main arm-could rise or fall freely-no weight could be added to it, even if desired, but it wasn't.

"My theory," Broadhead comments "is to keep the lap and the work in extremely intimate contact. This cannot be achieved by adding whole gobs of water on one side, with the lifting and tilting thus occasioned. The aim is to maintain an unvarying and strong suction (attraction). Then, with an extremely stiff lap backing, great pressure is automatically exerted on the high zones. The lap may squeal loudly at first but this subsides as the zones disappear."

A Wet uses much water and then adds much weight to squeeze it out. The Moist lets the forces of adhesion take care of this-and they are strong.

Shown copy on all the above and invited to correct any errors in it, Broadhead finds none but adds, "My only criticism is that the reader may get the impression that the technique is advocated principally for small-tool parabolizing; whereas it is of greatest efficacy in getting the desired starting sphere, and is later helpful in obtaining a smooth and comparatively zone-free paraboloid."

Considering the number of optical Wets there are, the above discussion should have important impact on amateur optics.

The Dry, or squealing porker, method may develop unexpected heat elsewhere. Your scribe, in polishing a mirror by hand with Barnesite, so highly perfected the "eeeeeeeeek" technique that feminine feet were wont to register violent objection by thumping on the floor above. The pig kept it up- he had a devilish glint in his eye-and the cellar door next flew open and a large tin wastebasket came hurtling down the stairway. A housebroken, domesticated pig, not a pigheaded pig might have taken this as a faint hint but this pig was trying to figure out just exactly what vibrates, and why, when a pig gets into a mirror. Probably every mirror maker has discovered pigs in his mirror and wondered whether harm would result. None, except on final figuring, where it makes too much heat. Don't let it go that far. Don't, even, hurry the moist technique; be deliberate.

With Barnesite, on its first try-out by your scribe several years ago, a 10" mirror polished out in just two hours. It is only fair to state, however, that it had received finings with Garnet Fines (Nos. 1, 4, 7) and would have polished out in fewer than normal hours even with rouge. It happened thus: Examination was made to see how the polish was coming up but it had already come up and was complete. Your scribe exclaimed: "Well I'll be damned!" (This, no doubt, is true.)

Cerium oxide is pink, in water suspension approaching white. It has long been known to be a possible abrasive but lay practically undeveloped commercially until the Barnes Company and other companies developed its application. Barnesite, which is even faster and, in fact the fastest known, is a special material developed exclusively by the Barnes Company beginning in 1941. It is a mixture of cerium oxide with other rare earth metal oxides. Barnesite is red-brown and costs a little more than rouge but what are a few cents' saving when a frogskin will buy enough cerium oxide and Barnesite to polish a dozen mirrors (many more, if the user will avoid the technique of the green mechanic with the diuretic oilcan).

"The general rule for any polishing materials," Ferson emphasizes, "is to apply only a small amount of polishing agent in a larger amount of water (a teaspoonful or tablespoonful in a glass of water); to forbear from adding more of the agent than the lap will handle; and not to try to hurry the action by adding more and more because this will not work.

"Just how much the lap will take up," he continues, "will depend on its hardness-the harder the less, until a very hard lap will take up none at all and will grind instead of polishing. Even a very soft lap will take up only so much in a given time. Toward the end of polishing, only water from the top of the glass, which contains the finest rouge, should be added."

LAST September this department announced that if as many as twenty five 16" Pyrex telescope mirror blanks could be ordered and molded at one pouring, the purchase price per blank would drop by about $100. This number of blanks soon were ordered and supplied to the users. A large part went to professionals who took advantage of the opportunity, and their co-operation is welcome. Some of these professionals formerly were amateurs.

This department now receives belated word that nine more 16" blanks are wanted, two of these from a worker who put off sending his shekels to Corning Glass Works till too late to get into the earlier club. Also, several who advised this department that they "had joined" apparently thought a mere expression of intention would serve, but Corning's mare won't go without the actual spinach. We now propose a 1947 "Sixteen-Inch Club" started off by the nine mentioned above. Present price is $37.50 per blank, f.o.b. Corning, N. Y., and a batch molding will take place at Corning when the other orders come in. If you don't feel equal to a 16" job now, perhaps you will later. Do not send any money to this magazine since business dealings are entirely with Corning, but if you wish, please let this magazine know you have joined its 1947 club, in the manner just named.

HOW thick, how rigid, must the glass tool be on which a mirror is ground and polished? On this there have been two schools of thought. One school says as rigid as the mirror, or almost. The other says rigidity makes little or no theoretical difference in a tool.

This question came up when this department was asked whether Corning's 5/8" or 1/2" Pyrex "Panel Stock," cheaper than mirror blanks though of the same glass, could safely be used as the tool for a fairly large mirror, say a 12-1/2". This stock is given standard commercial annealing but not the special annealing that mirror blanks rate. The question was passed to a few advanced amateurs. One replied: "I've been using tools much thinner than that but haven't noticed any astigmatism." Another: "Used a 1/4" tool on a 4-1/4" mirror. No astigmatism." A third: "I tend to side with the thin tool boys, provided the worker keeps rotating the mirror and circumnavigating the barrel." The last clause is the basis on which the thin tool school argument is based, but few appear to have risked loss of labor by making a planned experiment that would bring the answer out unequivocally, such as trying a 10" or 12-1/2" mirror on a 1/4" tool. Goat wanted.

YOU no doubt have made your formal will but, even then, what would your puzzled heirs know about disposing of your optical things? Pause and try to think out just exactly how mother, wife, or children would proceed with this job. You are an angel hovering overhead but you can't make your presence known and you are thinking, "There go my best eyepieces for a dime apiece and that fine little flat for two cents while they are trying to get $100 for that worthless unfinished, unfigured objective lens." You'd be thinking things no angel is supposed to think.

Would it not be a kind, thoughtful thing to jot down in pencil some informal notes on what to do with each item? Where to offer it. Value.

The total volume of optical stuff today thrown out or gathering dust because heirs don't know what to do with it probably would load a freight train. For a trifling favor one amateur's widow recently tried to give your scribe a microscope worth several hundred dollars, while another amateur who had promised his copy of Ritchey's rare classic "On the Modern Reflecting Telescope" omitted to implement his promise with a memorandum for his heir before he died (earlier than he expected) and the book was burned up and so is your scribe. Two examples of the crazy things that happen because heirs are left puzzled.

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