Acid etching

as a method for patterning glass came to Sweden in the late 1800s.
(There is information, not yet confirmed, that Kosta has etched glass in their catalogues from 1894 up to the 1970ies.)

The history of acid etching on glass
The Swedish chemist Carl Wilhelm Scheele is often called "the father of glass etching" - in 1771 he showed that hydrofluoric acid (HF) would mark glass.
Whether he, or others of his generation, did something with this knowledge is not known.

It seems that acid etching as a commercial technique started in he British glass industry some time mid-1800s, mostly used for matting surfaces.
There are horrible stories from Stourbridge about the working conditions:
"The worst was the aciding. In those days there were no fume extractors or ventilating fans and one had to have his acid vat out in the open air [...] The article could not be left in the bath of acid which was very strong, but had to be continually kept on the move by hand. Our faces and hands used to suffer from the srong fumes."

John Northwood I, working in Stourbridge during the late 1800s, invented several glass "machines", both for hot and cold work. Among his inventions were a couple of etching machines, machines that helped trace the pattern in the wax resist. While his machines undoubtedly speeded up the pattern-"scratching", they did nothing for the workers in he acid shed.
Anyway - during the time of JN I, the acid etching techniques were perfected in Stourbridge: there it was seen as a valid technique in itself, an alternative to engraving. (In Sweden acid etching has always been regarded as a way to mass-produce decorated glassware at minimal cost, as opposed to cutting/engraving.)
The sophisticated British etched pieces are almost exclusively matt, even though a mr Richardson is said to have discovered how to do "bright" (clear) etching.
(picture to the right: detail of a vase from around 1880, Th Webb & Son, Stourbridge)

In Sweden etching has been used either as matt or deep (which nearly always is bright/clear).

The basic principle is the same: the piece to be decorated is coated in wax where it is to be left un-etched. Then the piece is dipped in hydrofluoric acid (HF), the wax is washed off and, if the pattern is to be bright, he piece is dipped in sulphuric acid (H₂SO₄). (There are differing descriptions; some state the sulphuric acid dip should be done before washing, yet others say the dip can contain a combination of acids.)

- Both acids are very unpleasant, toxic and corrosive. There are horrible stories about bad conditions in Sweden, too: the only protection for the workers were rubber aprons and gloves, they had open vats and no extra ventilation. There are stories about the used acids being emptied into open ditches.
As far as we can understand, acid etching was regularly used in Sweden both for tableware and art pieces up until the 1980ies. It is still used in other countries, hopefully with better safety precautions.

 

Matt etching
For matt etching a paste was often used. The paste was made of ground fluorides mixed with water and various thickeners (glycerine, molasses, clay) to a viscous paste: it should be fluid enough to paint on, but not so fluid as to run.
So called "transfer etching" was also done with wax as a resist. Pattern templates were often made of steel, and the pattern wanted was left untouched - instead the surfaces meant to remain un-etched on the glass piece were carved away, to let the wax stick (compare book-printing techniques). The pattern was rendered in its actual size. Soft wax was spread onto the plate with a spatula, the wax was transferred to the glass with the help of a piece of paper. When the wax had cooled, the etching paste was painted on, left for some 10-15 minutes. The paste and the wax were then washed off in hot water. The result was a piece of glass with a matt patern.
We have written about transfer etching on our project blog (in Swedish), here. (opens in new window).
(There are examples of pattern plates and the resulting glasses in the exhibition.)

"Utility etching", as we are calling it here, is another method for transfer etching.

Nowadays (sand)blasting is used for matt finishes/patterns.

Deep etching
The pieces were first coated in hot wax (100-150 degrees Celsius), then left to cool. Next step was to scratch the pattern in the wax, the piece was dipped in hydrofluoric acid (HF) for a couple of minutes, next dipped in sulphuric acid to make it bright/clear (sometimes this procedure was repeated a number of times), finally the wax was washed off. Sometimes the etching fluid was a mixture of the two acids.

There were several methods to draw the pattern in the wax. Historically, a least in England and the European continent, this was done free-hand.
Later, different machines were developed - the first machines could only handle ("draw") one piece at a time.
The aforementioned John Northwood I was, allegedly, one of the pioneers. His first "machine" to do with etching was essentially a dividing machine: it held a template the operator was to scratch around, and helped find the next position for the pattern to be scratched. Later he invented a cogwheel-driven machine which could make drawings "automatically". It still exists in an (unfortunately unaccessible) museum magazine in the UK.
Probably it looks like the guilloché machines that became so popular around the 1890ies.

We think that the oldest Swedish machines were the so called guilloché machines (or needle etching machines), small mechanical wonders which could handle one glass at a time. The patterns were determined by a combination of cogwheels of various sizes.
A German manufacturer was called Kutzscher - we know that several Swedish glassworks bought from them. They made several different g-machines, some of which could handle all of 6 glasses at a time. Kutzscher provided pattern books complete with "recipes" (if one could understand the details...). Read more here.
On the page called A pattern book we show some handwritten recipes used at Kosta.

A couple of years ago we renovated such a needle etching machine. We wrote about that adventure (there is also a video) here (Swedish only; opens in new window)

In June 2017 we were given two, slightly different, needle etching machines. Read more about them here.

Pantographing is another method: a pantograph can handle several pieces at one time. We have two: one can take 24 glasses, the other can take 12. In the book Reijmyre 200 år, there is mention of one taking 36 pieces.
A pantograph is both more and less versatile than a guilloché machine, depending on the point of view.
A guilloché machine has the piece turn continuously, the needles never leaving the glass - thus there can not be patterns with "loose ends".
On the pantograph, however, he needles can be withdrawn from the glass at any moment; thus pantographed patterns can have lines that suddenly stop. The pantograph renders the pattern of the template, as many times (around the glass) as here are needles mounted.
A wonderful result of the construction of the pantograph is that one pattern template fits all sizes of glasses - with, for instance, 4 needles mounted, each needle operates in a sector 1/4th of a full turn. Further reading on "The pantograph, how it works". There is also a video.

As far as we know, acid etching has never been used as a complex patterning technique by the Swedish glassworks (as opposed to the British ones), but, all the same, it has been used for a long time - at Kosta from about 1890 to about 1980.
In one of the old catalogues from Åfors it is pointed out that the technique means cheaper decorated glass.

The Swedish glassworks have used both types of machines to prepare for etching.
The different construction of the machines lead to different pattern types. How to determine which machine has been used, see the page Guilloché or pantographed - are there pattern differences?

During the 1940ies the photographer John Selbing, working at Orrefors, started to experiment with yet another method to protect the glass surface from the acid. In 1952 he was granted a patent. Read more about Selbing and his method here.

We do not think etching has been done at Bergdala.

Sources:

• Hajdamach: British glass 1800 – 1914
• Kaijser: Anteckningar från studier vid Reijmyre Glasbruk
• Reijmyre glasbruk – formgivare, konstnärer och yrkesmän under 200 år
• Steenberg och Simmingsköld: Glas
• Steenberg: Servisglasets modellförändringar, from the book Modernt svenskt glas printed 1943
• Steenberg: Svenskt adertonhundratalglas
• Strömberg: Kostaglaset 1742-1916
• Northwood: John Northwood, his contribution to the Stourbridge glass industry, Stoubridge 1958