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Dip Mold

Privyprowlerz

Well-Known Member
Dec 12, 2015
110
0
I recently purchased a snuff bottle and wanted to check out the meaning of " dip mold " blown bottles.

quite interesting. these molds were made of various materials; wood, clay, metal or even a shaped hole in the
glass house floor. the key was to have the shoulder area larger than the base size so it could be pulled out of the mold
easily.
I got this photo from the sha.org site.

Jim



glass blowing dip mold .jpg
 

Harry Pristis

Well-Known Member
Jul 24, 2003
911
18
Northcentral Florida
I am skeptical -- despite the speculations of several authors -- that bottle molds were ever made of wood. Certainly not dip molds. A wood mold would have to be kept cool, below the ignition point of wood (374 to 500 degrees F) while in contact with molten glass at 2552 to 2912 degrees Fahrenheit.

To keep the wood below its ignition point, the story requires the wood mold to be wet with water. But, that moisture would flash into steam upon contact with molten glass, deforming the nascent bottle. In a dip mold, the steam would be trapped causing a violent end of the bottle and, conceivably, a jet of steam up the blowpipe.

Some wetted wood tools were used in glass-blowing (e.g. the battledore), but these are open tools which allow steam to escape.

I think the misconception started with Grace Kendrick (1968), an early collector who speculated about whittle marks and wooden molds:

WHITTLE MARKS (1820-1865)
German glass-makers used wooden molds which they kept wet to prevent from igniting.
This practice became popular in the United States after 182o. The custom began its decline when iron molds began replacing wooden ones after the Civil War, or 1865. All types of bottles were made in wooden molds, in which the bottles's shape had been whittled out by band.
The first bottles cast from these molds left definite tell-tale grooves in the outer surface of the glass. When looking through a "whittled-marked" bottle to the light, you can observe the markings left by the carver's knife (photo 6). They give the appearance of a cut-diamond and greatly enhance the charm of the bottle.
Collectors who are intrigued with the beauty of bottles, will prize these as their most valuable (Photo 7). The number of these bottles in existence is limited, and they can be considered fairly rare.

Later authors cite Kendrick. I think Bill Lindsay has this wrong when he says:

Wooden dip molds - another common pre-19th century mold material - had to be kept wet in order to survive long the intense heat of molten glass. This allowed steam to form in between the hot glass and mold surface causing the glass to "ride" on the steam cushion making the evidence of molding often very difficult to distinguish from free-blown bottles. Sometimes the expanding parison would touch the sides of wooden mold before the cushion of steam formed leaving ripples, though this feature may be impossible to positively distinguish the use of a wooden mold versus glass imperfections (e.g., whittle marks) caused in metal molds for other reasons (A****er 1893; Tooley 1953; Kendrick 1968; Toulouse 1969b; Jones & Sullivan 1989; Van den Bossche 2001; Deiss pers. comm. 2005).

Cecil Munsey in his 1970 book, speaking of ancient containers is more circumspect in asserting that:
As to the exact materials of which these ancient molds were made there is room for speculation. One example of a stone mold has been found. In addition it is logical to assume the usage of ceramic, bronze, and wood."

For commercial production, the brass mold was introduced in the late 1700s and there was a change to iron molds in the 1800s.

Even Van den Bossche (2001) allows for the possibility of wood, but he does not distinguish between bottle dip molds and tools like the battledore. Van den Bossche
in his glossary defines "mould" as "a metal, ceramic, or wooden form . . . ."



 
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andy volkerts

Well-Known Member
Jan 10, 2005
2,833
0
Sacramento, California
I looked up Oak wood and its ignition point without open flame is 900 degrees fahrenheit, still a lot colder than molten glass, I agree that dip molds were probably not made of wood, but wooden molds were used at Colonial Williamsburg in there glasshouse, at least that is what is stated at their site. The molds were prepared but did not go into details as to what that preparation might have been. I am skeptical like Harry that wood was used as a mold medium for bottles.......Andy
 

Harry Pristis

Well-Known Member
Jul 24, 2003
911
18
Northcentral Florida
Errors that find their way into print may take on a life of their own. Other authors rely on the erroneous information and publish it as fact, often without citing the source. It can be difficult to stamp out a false fact after multiple authors repeat it.

As for the ignition temperature of oak, published ignition temperatures for wood are all over the map. In a survey of published studies, the reported temperatures
"...span 210–497ºC [410F--926.6F] for piloted ignition and 200–510ºC [392F--950F]for autoignition. The following reasons should be considered that might account for the spread:
• the definition of ignition that is used
• piloted vs. autoignition conditions
• the design of the test apparatus and its operating conditions
• specimen conditions (e.g., size, moisture, orientation)
• species of wood."

Babrauskas, V., Ignition of Wood: A Review of the State of the Art, pp. 71-88 in Interflam 2001, Interscience Communications Ltd., London (2001).
 

Privyprowlerz

Well-Known Member
Dec 12, 2015
110
0
I would agree Harry. doesn't really make sense that wood was used, but it's really hard to
say what went on during the early days of glass blowing. love the discussion.

Jim
 

RJ2

Well-Known Member
Mar 6, 2016
62
0
Cool discussion.

The missing key, I believe, is a "burning in" process where the wood mold is conditioned by blowing an initial to be scrap bottle (glass pieces).
That along with steam vents and I can see wood molds being used commonly.

The posted photo is a:

" traditional full height wood mold made of cherry by Walter Evans (who has stopped making them since the loss of his assistant.) It has a disk bottom attached to one side and hinges and handles to permit an assistant to open and close the mold around the glass. The mold is burned in by blowing glass pieces not intended to keep. It has holes drilled to allow the steam to escape and is stored in water between use. The glass is inserted, the halves closed and the glass allowed to settle near the bottom before blowing and turning fill the volume. When the glass is removed it has crisp shape and may require no further work on the body or hot bits for handles or decoration may be applied. The piece must have the lip worked
. "

Reference: http://mikegigi.com/molds.htm
 

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Last edited:

Harry Pristis

Well-Known Member
Jul 24, 2003
911
18
Northcentral Florida
Cool discussion.

The missing key, I believe, is a "burning in" process where the wood mold is conditioned by blowing an initial to be scrap bottle (glass pieces).
That along with steam vents and I can see wood molds being used commonly.

The posted photo is a:

" traditional full height wood mold made of cherry by Walter Evans (who has stopped making them since the loss of his assistant.) It has a disk bottom attached to one side and hinges and handles to permit an assistant to open and close the mold around the glass. The mold is burned in by blowing glass pieces not intended to keep. It has holes drilled to allow the steam to escape and is stored in water between use. The glass is inserted, the halves closed and the glass allowed to settle near the bottom before blowing and turning fill the volume. When the glass is removed it has crisp shape and may require no further work on the body or hot bits for handles or decoration may be applied. The piece must have the lip worked
. "

Reference: http://mikegigi.com/molds.htm
Thank you for the link, RJ2! I'll have to be more cautious, I see. The wood hinge-molds were made by Walter Evans in 1999 or thereabouts. There was no reference to early use of wood molds, but we now know it can be done.

"Burning-in" the wood mold must refer to getting a uniform carbonization of the interior of the cavity, it seems. It may be that the carbonized wood insulates, to some degree, the rest of the wood block.

From now on, I can only argue that wood was never used for bottle molds in any high-production, industrial situation. I think wood is for artisans and artists, not for the production line. :D

 

andy volkerts

Well-Known Member
Jan 10, 2005
2,833
0
Sacramento, California
Well, Live and learn. Carbonization must have been the " Preparation" mentioned by Colonial Williamsburg for the wooden bottle molds that they used. They were definitely not a high production producer of glass in the early days.......Andy
 

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