Flashing

Not sure if this is the forum for this question but here goes-
I had a question about flashing or incasing a clear bottle in another color. I searched the Historic Glass website but did not find anything. I sure it was not a common practice on ordinary bottles. I understand that it was a cheaper way of making a colored bottle without the expense of coloring a larger batch of glass.
They gather up clear glass then dip that in the colored glass before blowing the bottle.
I have a couple in my collection. One is a fairly modern Pyrex apothecary that is flashed with red. The other is late 1880's , ground pontil, and is flashed with emerald green.
That is the one I have problems with. This one seems to have the colored glass on the inside. If you look close some of the color is missing on the neck where the glass was ground for the stopper. If you look at the bottle at eye level, as it sits on the shelf, you can see that the entire, thick base of the bottle is clear except on the bottom inside. It is a strange bottle as it looks like an bright emerald green until you get to the bottom. It is the only one I have had that has the color on the inside.
I would just like to know if any one has any information on flashing of bottles. I think I have heard it called casing too. I know it was used alot in cameo glass but that started out with expensive glass all around.

Hi "bostaurus" and you are right about the Historic Bottle Website not including any real information on "flashing." It just wasn't something done at all with common, utilitarian bottles so I haven't covered it at all, although I should at least add some mention of it to the Glossary page. It wasn't too uncommon with what I call "specialty" bottles like the two example you note.

According to my Handbook of Glass Manufacture (Tooley 1953), other terms for flashing (which was a glassmaker term also) were "striking" and "cased glass"...your noted term "casing" for short on the last one I guess. The definition of cased glass is "glassware whose surface layer has different composition from that of the main glass body." Flashing is "applying a thin layer of opague or colored glass to the surface of clear glass, or vice versa. See also striking." Although this doesn't say how the glass is applied but is what the proper term for your items is.

Striking is defined as "development of color or opacity during cooling or reheating." This is different than applying glass but points out that glass colors are influenced by more than just the chemical composition of the batch itself.

I remember Toulouse noting that a regular batch of bottle ("green") glass could be made very blue (deep blue green) or true green to aqua green during the same day by having a "reducing flame" or an "oxidizing flame." This could result in the early morning items (after a night of banking the fire under the pot with the air vents shut down) being very blue in color with those as the day proceeded being green (or aqua) blown from the same batch of glass! That explains some of the wide ranging variety of bottle colors (like the array of blue to blue-green to green Henley's IXL Bitters out West here) and the fact that they didn't have to be blown from different batches of glass, but could have been blown on the same day from the same batch of glass.

Sorry, I digressed there...unfortunately, Tooley's great book noted above doesn't tell how to do flashing except as implied by the definition - that a thin layer of glass is applied...dipping being the most likely it seems, as you noted.

However, Frank Kulasiewicz's book "Glassblowing - The Technique of Free-Blown Glass" (and excellent book BTW) does include a description of the process of "Striking or flashing a colored glass..." (page 143). In short, it is a "chemical reaction in molten glass that leads to the formation of particles of colloidal size precipitating out of the saturated glass." Now what does that mean?

It appears that the striking method of flashing is done more by various heat treatments to specific chemically composed glasses, not dipping (although I think that can be done to?). More specifically, "..the striking process is complicated and often depends on special heat treatments to start the crystallization process and special chemicals to reduce the metal out of the melt or to act as the nuclei for growth."

He, at the end, makes reference to it being a "art" and hard to describe in that "...complicated theories have been published, yet these do not dispel the magic of clear glass suddenly becoming colored."

Sorry for the long response here but wanted to figure it out for myself so that I can add something to my Glossary page about the subject. I already cover "flashing" very briefly there, but need to expand it a bit to cover the "striking" possibility. So I guess the bottom line is that it could be applied glass (how, isn't specified) or done through the striking process vaguely outlined in "Glassblowing...". Glass is such an interesting substance, eh?

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Well you have all done it again. This is an interesting subject because I have some Bohemian vases that were obviously flashed with ruby red with deer and sceinery cut to the clear base glass. I also have some cameo glass work pieces.
Thanks for the book references Bill, I have put them on my books to get.doc file. At least I can start with the library down town.

It is hare to get a lot of information on the "HOW IT WAS DONE!" subjects that I am always looking for. Thanks - RED Matthews

I do find the whole process of bottle/ glass making fascinating. The information on "striking" was new to me but I really should have thought of it before. I am a potter in my spare time and the same process applies to glazing. Glazing is basically the application/formation of a glass layer on the pot. Reduction/oxidation plays a very big part in the color that forms in the glaze. For reduction all openings where oxygen can enter the kiln are plugged after the kiln reaches high temp. The chemicals respondsible for color (copper, iron, cobalt,etc) have no oxygen molecules to bind to. In oxidation they allow oxygen into the kiln so now the chemicals can form oxides. Some copper glazes will be red in reduction and blue in oxidation. There will also be variations of a glaze within the kiln due to differences in the amounts of oxygen and other gases in different areas of the kiln.
As one of the people you mentioned said "it is more of an art". Professional potters work for year to perfect a certain glaze and it still may not work correctly everytime or for someone else.
He also talked about crystals forming..there are special glazes that will form crystals if fired correctly and cooled in slow process. I don't think this is quite the same as in glaze this forms an actual pattern within the glaze rather than changing the color.
I would really like to know if you guys find out any more information on the subject.
I will send pictures of the bottles when we finally get back to the States and I can unpack them.

Hi again Red & "bostaurus"....I would love to see images of the bottles you noted bostaurus! I've seen things like Red has noted in antique stores...particularly red "flashing."

Kulasiewicz also notes about the flashing/striking process that "To strike a color requires a knowledge of the glass, the furnaces, and the appropriate time/temperature sequence...Ideal timing and measuring might exist in the laboratory, but it seldom exists where the craftsman works. Despite all that has been written on the various strike colors, it is still up to the craftsman to get a feel for the process."

That fits the "art" aspects of that type of work that you noted too. What I would love to find are some of the "...all that has been written on the various strike colors..." information that the Kulasiewicz mentions! I'll check the references in his book.

All my bottles are stored at my in-laws. We land there late July before moving on to 'who knows where'. I will dig though the boxes and get some pictures of the 'flashed' bottles for you.
Thanks for the information.

Finally got the bottles unpacked, photographed and repacked. Unfortunately they will have to stay here as there is not enough room in the van to take them with us to Maryland.
I took some pictures of the green flashed bottle we had discussed but the picture down load will have to wait until we get our household delivered and computer unpacked.
Having looked closer at the bottle it appears that the green class was dipped in clear glass and then blown. I always thought it was done the other way around...the clear glass dipped in colored glass.... hopefully I can post the pictures for you before too long. It is a beautiful color.
I also have a red one for you to look at.. I don't know if it is flashed or not.

Looking forward to the images when you get home.......Bill

finally have the computer unpacked and pictures downloaded.
This is the green bottle I was talking about. You can see in the neck where the green glass on the inside has been been ground away when they fit the stopper.

This shows the that the green is the inner layer of glass.