The Polishing of Cut Glass


  The Traditional and Modern Methods of Polishing


Approaching a generous display of American Brilliant Period cut glass at an antique show, the show-goer is often nearly overwhelmed by a welcoming mass of glitter. If he is a collector, he soon searches for a pattern — a familiar one perhaps, or one that is “in the books” — or he looks for a particular shape. But before he has had a chance to examine any such article for damage; before the quality of the blank has registered in his mind; and before the accuracy of the article’s cutting has become a matter to be closely inspected, our hypothetical collector will have considered — consciously or unconsciously — that glitter that so welcomed him.

If he has had considerable experience with cut glass, then our collector will have also considered the “quality” of the glitter. It is not surprising that the result of the final stage in the production of cut glass — the polishing of the cuts that have felt the action of the smoother’s stone wheels — becomes the first attribute to be noticed when viewing cut glass. Polishing can often determine whether an article is — or is not — a desirable purchase. An excellent piece of cut glass can truly be “ruined” by careless or indifferent polishing. Especially vulnerable to misuse is the modern, chemical method of polishing that uses acid baths. When correctly done, however, the result is comparable to the traditional, mechanical method of polishing, often described simply as “by hand.”

In the mechanical method of hand-polishing, successive applications of pumice and metallic-oxide polishing powders such as jeweller’s rouge, are mixed in water and applied to polishing wheels by “feeding up” the mixtures by hand from trays beneath the wheels. When the mechnical method is used today — as in the repair of cut glass – – cerium oxide is usually substituted for jeweller’s rouge. It is said to give a better result and it is less toxic. The present-day cutter typically uses wheels of hard felt; in the past, wheels made of fruit wood were used. 

                   The Art of Polishing Glass by George F. Latham

(N. B.: The following article contains the entire utility patent, no. 230,137, granted to George F. Latham on 20 Jul 1880. The patent application was accompanied by “specimens” but no illustrations. The year 1880 is an early date for a proposal to use acid as a polishing agent. Apparently Latham’s proposal was not widely adopted.)

To all whom it may concern:

Be it known that I, George F. Latham, of Sandwich, of the county of Barnstable and State of Massachusetts, have invented a new and useful improvement in the Art of Polishing Cut Glass; and I do hereby declare the same to be described as follows:

Heretofore, in order to polish glass after it may have been cut or ground by a wheel or other device generally employed for such purpose by glass-cutters, it has been customary to effect the finishing or polishing by means of buffing or polishing wheels or implements and suitable polishing materials, such as pumice-stone, rotten-stone, or oxide of lead, or “putty” as termed by glass-cutters.

This process of finishing is attended with the formation, in the surface of the glass, of extremely minute scratches or grooves, which cannot be avoided, owing to the substances and means employed in the reduction of the glass. These scratches or grooves (generally invisible to the eye of an ordinary observer) materially affect the reflective powers of the surfaces, often causing them to appear more or less greasy or imperfect, and besides they more or less impair the refractive properties of the grooves or prismatic surfaces or part of the ornamentation of the glass.

The purpose of my invention is to obliterate the minute scratches or grooves of the polishing process, or so modify the surface so polished as to prevent the evil results thereof and cause it to present a highly brilliant appearance; and this I do by combining the ordinary process of wheel or hand grinding and polishing, as mentioned, with the application to the surface or surfaces so treated of a mixture or bath of fluoric and sulphuric acids, using, by preference, seven parts, by measure, of the fluoric acid and two parts, by measure, of the sulphuric acid, to which, in some cases, one part, by measure, of water may be added.

Into a bath of such composition, after an article of glass may have been wheel or hand cut and polished, I dip such article and allow it to remain therein for a very short space of time — viz., about two minutes — after which, and having removed the article from the composition, I wash from the surface of it acted on any adhering acid and superfluous matter or matters, in which case the minute scratches or grooves resulting from the wheel grinding and polishing will be found to have been obliterated or so changed as no longer to produce the bad effects as stated, the whole surface of the glass having a far more brilliant appearance than can be produced by the hand or wheel polishing process alone.

The fluoric acid alone will not produce the desired result. I have found in practice that in order to attain it an amount of sulphuric acid, or some equivalent therefor, must be combined with the fluoric acid.

I do not confine my improvement to the using of the above-described acids in the precise portions hereinbefore mentioned, as they may be varied therefrom somewhat, and still be productive of a good result.

I am aware that for some years prior to my invention it has been customary to use a mixture of acids, as described, in the process of etching glass in order to produce ornamental figures thereon; but my process is not for such purpose, but is to overcome a difficulty or difficulties incident to or resulting from the ordinary modes of hand or wheel cutting and polishing of glass.

What I claim as my invention is as follows, viz.:

1. In combination with the ordinary hand or wheel cutting and polishing of an article of glass, the subsequent treating of it by acids, as described, all being substantially as and for the purpose set forth.

2. As an improved manufacture, glass, wheel or hand cut and polished and susequently finished by acids, as set forth.

                  Additional utility patents concerning the polishing of cut glass are as follows: (All patents are available from USPTO)

  • Patent no. 226,054: Brush-Wheel for Polishing Glass. Daniel Forbed, 30 Mar 1880.
  • Patent no. 283,273: Apparatus for Supplying Abrading and Polishing Material to Cutting and Polishing Tools. John S. O’Connor, 14 Aug 1883.
  • Patent no. 386,417: Feed Apparatus for Glass-Polishing Machines. Richard Thirsk, 17 Jul 1888. 

                   Contemporary Discussions of the Chemical Method

In the real world it is often difficult to tell the difference between mechanical (hand) polished and chemical (acid) polished cut glass when each is well done. General statements — which are of limited use — usually stress that the hand process results in a “softer” look than the acid process or that the acid technique presents a “hard” glitter. While this comparison is often true, the “look” of an acid-polished article can sometimes be very close to that produced by hand-polishing. As described in the paragraphs that follow, this is accomplished, in part, by some hand-polishing of acid-dipped objects. While various writers contend that acid has the advantage of being able to polish the tiniest cuts more completely than the hand method, when rotating brushes are used in addition to the solid wheels the mechanical technique can also do an effective job.

Like other aspects of the glass business, details of the acid-polishing techniques used during the Brilliant Period were closely guarded by the factories that used them. Therefore, written accounts are rare, and are usually incomplete. The extract given below provides a comprehensive account of the process, and it answers many of the questions that have arisen in modern times. The article is part of one that was published in the June 3rd 1915 issue of Crockery and Glass Journal. It, in turn, is a copy (or more likely a paraphrase) of an article entitled “The Industrial Uses of Hydrofluoric Acid” written by K. F. Stahl that appeared in the Journal of Industrial and Engineering Chemistry, The date of this issue of the Journal is not as yet known. To estimate the date mentioned in the article, this writer has simply calculated a date using the year the paraphrase was printed, 1915. This ignors the influence, if any, of George F. Latham’s patent of 1880.

[Acid-polishing] started about eighteen years ago [i.e., before 1897] and is at present probably in use in all of the cut glass factories in this country, of which there are quite a number, and some of them rather extensive. At first some manufacturers claimed that glass treated by the old process had a better polish. They were soon convinced, however, that cut glass polished with acid had a finer lustre and edges.

The last operation in manufacturing cut glass is the polishing of the surfaces which have previously been cut into the glass. This was formerly done with oxide of iron or oxide of tin. As every plane had to be polished separately by skilled labor, it was slow and expensive work.

A finer polish is now obtained in the following manner: For vases and similar shapes, where the polish is required only on the outside, a wooden stopper is cemented in water-tight with paraffin or wax. Other surfaces which are not to be touched by the acid are also covered with asphaltum, wax, or some similar substance. It is essential that all surfaces to be polished must be absolutely clean, and especially free of every trace of grease. To accomplish this they are brushed with soda solution by girls who wear rubber gloves; then they are washed in clean water, and after most of the water has dripped off, they are dipped in the acid bath.

Generally a mixture of one part by weight of sulfuric acid, 66 degrees Beaume, with three parts 60 per cent hydrofluoric acid is employed. This mixture is in a lead vessel large enough to submerge the largest pieces to be polished. It is placed directly in front of a ventilating tube, through which a ventilator creates a strong suction. This protects the polisher from the strong vapor given off by the acid mixture and he needs only a rubber apron and long rubber gloves for his protection. The perfectly clean and partly dried-off pieces of glassware are held one at a time from one-half to one minute in the acid, and then immediately dipped into the water.

By the action of the acid on the glass, a thin crust is formed consisting of calcium fluoride, probably with some sulfate of lead and sodium of potassium fluoride. This is removed by brushing with water, after which the pieces are washed off in clean water and dipped again in the acid. The polish is usually complete after three dippings. Every piece is carefully inspected, and defective spots are polished by hand. If the grinding was carefully done, this is rarely necessary.

It is not at all certain that all manufacturers triple-dipped their articles. Other writers imply only a single dip.

The use of wax to protect uncut surfaces from the action of the sulfuric/hydroflouric acid mixture is also mentioned in a second article, published in the December 20th 1917 issue ofCrockery and Glass Journal. After dipping, the wax was removed “with hot water”.

                    (The writer greatly appreciates receiving copies of the foregoing articles from Craig Carlson.)

                    Cut Glass versus “Processed Glass,” an opinion from Higgins & Seiter, published in the company’s Catalog #10 for 1899-1900 (p. 1-2):

Both the monetary and artistic value of Cut Glass depend entirely upon the amount and kind of labor by which it has been ornamented.

The raw material — the dish or decanter, goblet or pitcher, in its plain state is comparatively inexpensive.

It will hold wine or water just as well — but so will a stone jug or a tin cup.

People are willing to pay more for Cut Glass simply because of its great, its almost incomparable beauty. Not even the precious metals themselves lend such enchanting brilliancy to a table. It flashes, and sparkles, and radiates, and corruscates like nothing but diamonds of the finest water.

This gift of beauty is bestowed upon what would otherwise be almost lustreless material by the painstaking toil of long-experienced workmen. With wheels of steel and stone and wood, the constant drip of water, the application of various secret wearing substances, and the most careful, watchful touch, the intricate designs are cut and smoothed and polished, till slowly, line by line, hour by hour, and often day by day, what was a thing of mere utility becomes a work of art.

All this necessarily entails expense, for to the certain expenditure is to be added the risk — as not unfrequently happens — of an untoward pressure by which the work of days is instantly shattered into worthless fragments.

No one, in fact, who has ever been permitted to enter the barred doors of a glass cutting establishment and watched the long and intricate process by which this favorite product of human skill is brought to slow perfection, will ever regard its cost as anything unreasonable.

Thus far we have referred exclusively to real glass cutting. There is an imitation.

In the insatiate desire to substitute pinchbeck for sterling, counterfeit for genuine, veneer for solid wood, a way has been discovered to produce a temporary cut glass effect by a much shorter method. After the design has been roughly beveled out, the portion of the glass not to be acted upon is coated with wax, and the article immersed in an acid bath for from three to perhaps fifteen seconds. In this time the action of the corrosive liquid is powerful enough to give the surfaces, which under the regular method would take hours and days to polish, an appearance of brightness. The article is then dried, and in many instances, with no further ceremony, thrown upon the market as “Rich Cut Glass!”

Of course, it isn’t anything of the kind, any more than a rhinestone is a diamond, or iron pyrites the gold of Ophir.

It is simply the glass “in blank,” as it is called, worth say forty cents per pound, plus the labor of roughly routing out the design, plus a fifteen-second plunge in an acid bath.Practically all the labor, most of the time, certainly all the skill which gives real Cut Glass any value or any lasting beauty, is lacking.

Those who know cut glass thoroughly have no difficulty in detecting the acid process, even when the article is entirely new. For unless, as in some cases, a little pain has been taken to supplement the bald effects of corrosion by tooling the most glaringly defective surfaces, there is a greasy shading — a betraying dullness, never seen in reputable hand work.

It is, at best, no better, and, as we believe, no more lasting than a lacquer, and should be rated only one grade high, either in price or quality, than ordinary pressed glass.

And yet it imposes on a great many people and dealers whose consciences do not appear to trouble them, actually encourage the imposture, and make money by it.

But let others do as they may in regard to this acid-bitten glass, we are convinced that for Higgins & Seiter there is but one course to take, and that is not merely to discredit it to our customers, but to have nothing to do with it, in any shape, form or fashion; to exclude it entirely from our stock; not to handle it at any price, or on any pretext.

With us, therefore, if with nobody else, cut glass will continue to mean glass cut and polished exclusively by hand, in the old-fashioned and only artistic way — not processed glass, costing and worth only a fraction of the real article.

And where, hereafter your may see “Cut Glass” advertised at prices suspiciously below what the genuine article is sold for here, you will know the reason why.

Meantime, hand-cut, hand-polished glass, in its most beautiful and varied as well as as its simpler forms, will continue to be sold by us, as usual, “at least one-quarter less than elsewhere.”

Higgins & Seiter.