What is the difference between free blowing and mold blowing

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July 3, This has the effect of forming an elastic skin on the interior of the glass blob that matches the exterior caused by the removal of heat from the furnace. The glassworker can then quickly inflate the molten glass to a coherent blob and work it into a desired shape.

The Toledo Museum of Art attempted to reconstruct the ancient free-blowing technique by using clay blowpipes. The result proved that short clay blowpipes of about cm facilitate free-blowing because they are simple to handle, easy to manipulate and can be re-used several times.

Contemporary glass artists most often work with free-blown methods because they offer the greatest artistic control over glass sculpture making, and they give artists the freedom to experiment with unique designs. Mold-Blowing Mold-blowing was a technique also developed by the Romans sometime after the invention of free-blowing, probably in the first century A.

Like with free-blowing, molten glass is handled on the end of a blowpipe — but rather than shaping and twisting the gather with air, the glass is immediately placed into a pre-designed mold of wood or metal and then blown to the appropriate measure. When cooled, the glass can be removed by lifting or separating panels. Mold-blowing is more commonly used for functional glass art pieces, like tableware, or to produce uniform reproductions of the same design.

With the pontil holding the bottle, the blowpipe used for the development of the bottle could be removed to allow finishing Click empontilling and cracking off to see an illustration of these processes. By far the best, and as a result the most popular, method of severing the blowpipe from the bottle is a process known as wetting off.

Wetting off is merely marking with a wet wooden paddle around the neck of the hot bottle where it is attached to the blowpipe. The cold water weakens the glass in the desired spot and a sharp tap by the gaffer breaks the bottle free from the blowpipe.

Another popular method of severing the blowpipe from the bottle is by cutting the neck with shears Munsey One of the better books covering the process of blowing bottles and glass, with scores of pictures, was Grace Kendrick's " The Mouth-Blown Bottle. Empontilling: A pontil mark is a variable size and type of scar left on the base of a bottle by a pontil rod.

A typical pontil rod or "punte" "punty" was a long feet rod which was securely attached to the base of the just blown hot bottle. A pontil rod held the bottle during the steps in the bottle blowing process where the blowpipe is removed cracked-off from the bottle and that break-off point is "finished", i.

Once the bottle is "finished", the pontil rod is sharply tapped which breaks it free of the bottle. The base of a bottle which was held with a pontil rod will almost always retain some evidence of the pontil rod attachment.

The following description of this process is from an patent U. Patent 51, for an "Improved Clamping-Punty" - a patent for one of many improved grasping devices which replaced the pontil rod and were a much quicker method of holding a bottle by its base for finishing.

It is the most succinct period description of the use of a pontil rod the author has run across. As discussed later, various non-fusing, bottle base grasping tools snap or snap-case tools were already in use by glassmakers in the U.

In the manufacture of glass bottles great difficulty has been experienced in holding the bottles in a proper manner for finishing the necks. The common mode heretofore employed has been to use a straight bar or rod of iron with a head or ball upon one end, to which, when it is dipped into the melted glass, a quantity of glass adheres.

While in a semi-fluid or plastic state, and while the bottle is also in a plastic state, immediately after being withdrawn from the mold, the glass upon the rod or punty is brought in contact with the base or bottom of the bottle and immediately it adheres thereto, and the glass soon chilled, the bottle is made fast to the punty, so that the operator may finish the neck of the bottle in any desired form.

It will be recollected that during the process of uniting the punty to the bottle the bottle is in a plastic or flexible state in consequence of the heat it still retains after having been withdrawn from the mold, thus rendering it liable to get out of shape. Another objection to the old method is that when the bottle is completed the portion of the glass adhering or connecting the bottle to the punty is broken by a sudden jar by the operator, which leaves a rough place on the bottom of the bottle.

By our invention we obviate all the difficulty attending the old method for finishing the necks of bottles. Pontil rods and the resultant pontil scars go back to antiquity, having been used for bottle making as early as Roman times McKearin All of the different pontil scars noted below are usually but not exclusively found on American made utilitarian bottles that date to or before the American Civil War mids. Pontil scars of all types became ever increasingly unusual on utilitarian bottles as the s progressed and largely disappeared by the late s or early s as various "snap" or snap case tools dominated the task of grasping the hot bottle for finishing the snap case is covered later on this page.

For example, this author in inspected examples of a large majority of the bottle types recovered from the S. In addition, the bottles from the S. Republic , which sunk off the eastern U.

However, the transition time for conversion from the pontil rod to the snap case was lengthy. The first use of the tool in the United States may have been in the s, but its use was definitely evident by at least the early s. The following outlines the basic types of pontil scars and how they were formed. For much more information consult the Pontil Marks or Scars page. Glass tipped Pontil : This type pontil scar was formed by the use of a solid iron bar as the pontil rod. One slightly widened end of the bar was tipped with molten glass then applied and fused to the base of the bottle.

A glass tipped pontil rod made contact with most or all of the bottle base within the confines of the diameter of the pontil rod tip. Click HERE to view an illustration of a glass tipped pontil in action.

When the rod was broken free of the bottle, a generally round but fragmented scar was left behind on the base of the bottle. This is usually manifested primarily by an assortment of glass fragments protruding above the base of the bottle.

In addition, the rod would usually take with it some small glass fragments from the base of the bottle leaving a scar which is a round scattering of "bumps and gouges" without a distinctly unmarred center - like the blowpipe pontil scar described below. Click on the picture to the left to see an enlarged version of a typical glass-tipped pontil scar that shows the detail better. Click sauce bottle to view a picture of the entire bottle. The glass tipped pontil scars are usually about the same diameter of the orifice or upper neck of the bottle - like the blowpipe pontil scar which is discussed next - but for reasons unknown unlike the blowpipe pontil scar which is explained next.

For more information click glass-tipped pontil. Blowpipe "Open" Pontil : This type of pontil mark - which was also called the "ring pontil" - was formed when a hollow blowpipe was used as the pontil rod, is at least as common on American made bottles as the glass tipped pontil mark Boow The use of a blowpipe doubling as a pontil rod dates back at least to the midth century in Europe McKearin This was likely done to both save on the number of tools used by the glass blower and to save time.

Blowpipe pontil scars were likely formed by two slightly different processes which would each be indistinguishable on the finished bottle:. Click HERE to view an illustration of a blowpipe pontil in action.

When a blowpipe was used as a pontil, it left behind a distinctive ring shaped scar that is usually sharp edged, round to slightly oval, with a hollow in the middle that is roughly the size of the bottles orifice circumstantial proof that one blowpipe was usually used for both blowing and empontilling. Click HERE to view a picture of this entire bottle.

For more information click blowpipe pontil. Sand Pontil: The sand pontil scar was also a common method of empontilling a bottle for finishing, though somewhat less common on American made bottles than the other three primary methods described here.

This mark was formed when the hot glass on the tip of an iron pontil rod with a flared end was dipped in sand or glass chips prior to application to the bottle base. The sand was apparently intended to keep the pontil rod from adhering too closely to the bottle, facilitating easier removal. However, a larger connecting surface at the end of the pontil rod was necessary with this method in order to ensure an adequate adherence to the bottle base Jones The picture to the left is of an English made spirits bottle with a typically diffuse sand pontil, which are the multitude of small scattered specks outlining a rough circle within the middle portion of the base.

Click HERE to view the entire bottle. Click sand pontil base to view another picture of a sand pontil on the base of a ca. For more information click sand pontil. Bare Iron Pontil : This type of pontil mark is the result of using a bare iron pontil rod with an appropriate shaped tip or head which was heated red hot and directly applied and fused to the base of the bottle to be held.

There was no glass added like a glass tipped iron pontil rod or remaining like using the blowpipe for a pontil on the iron tip of this type pontil rod.

Click HERE to view an illustration of a bare iron pontil attached to a bottle base. Like the other pontil rod types, this one was probably removed by sharply tapping the rod near the attachment point. The iron deposits which form the iron pontil mark are very small fragments or residue from the tip of the bare iron pontil rod itself.

The picture to right is a particularly distinct iron pontil mark with ample residual iron left imbedded in the bottle base.

For much more information click iron pontil. For lack of any previously defined term, it is being called here a "combination" pontil scar.

Only a small minority of pontil scarred bottles have "combination" pontil scars. The bottle pictured to the left has an obvious bare iron pontil mark surrounded by a distinct glass tipped pontil scar click on picture to enlarge for detail. Click umbrella ink to view a picture of the entire bottle. The reasons for this phenomena are unknown since the bottle only needed to be held by one rod for finishing. The most likely answer is that the center of the glass tipped pontil rod fused to the hot base of the bottle leaving behind the iron oxide typical of a iron pontil scar along with scattered fragments of glass typical of a glass tipped pontil scar.

There is at least one other combination pontil variation; for more information click combination pontil. Many different designs of these tools were used though the tool illustrated to the right would be typical of the general snap case design. Click on each picture to enlarge to a better quality version. Instead of affixing a pontil rod in some fashion to the base of the hot, now molded bottle as described above the handler or servitor used one of these non-empontilling tools to hold the bottle.

These tools usually left little or no markings on the bottle base or sides. Sometimes a bottle will appear to have the surface texture of the body sides indented or roughed up by the tool or the sides slightly flattened by over-compression. It is usually difficult or impossible to conclusively differentiate the subtle markings of a snap case or sabot from the array of possible mouth-blown mold or glass making imperfections.

The sabot also called a "spring cradle" was the earliest version of a non-empontilling i. This four-pronged tool was sized to closely fit the diameter of the base and lower sides of the bottle with different sized sabots apparently necessary for different diameter bottles.

The sabot likely made its way to the U. An illustration of the sabot can be found in the book Antique Glass Bottles - Their History and Evolution by Willy Van de Bossche which is still widely available. A snap case was also known simply as a "snap" or as a "spring punte. The three separate pieces were held together by a tubular sheath which when pushed up towards the bottle "snapped" closed onto the sides and base see illustrations above.

A collateral benefit of the snap case is that it more securely held the hot bottle than any of the other methods allowing for the development of more sophisticated finishing tools Deiss Various types of snap case tools were used in the manufacture of mouth-blown bottles up until semi-automatic and automatic bottle machines effectively ended mouth-blown production and the need for such tools.

An example of a relatively early patent November for an "Improved Clamping-Punty" is viewable at the following link: U. Patent 51, This particular tool had a long handle with a spring on the inside which apparently opened and closed a "conical ring" at the business end of the tool. An patent granted to Joseph B. Patent Office a.

For more information on the subject of snap case tools, consult the Bottle Bases page. Mold -Blown Manufacturing and related. This section deals with mouth-blown bottles that were not fully free-blown, but instead manufactured by processes where the bottle shape was formed substantially or entirely by some type of single or multiple part containment mold. An example of a "two-piece" mold from a glassmakers catalog is shown below left. This section also discusses various other mouth-blown bottle manufacturing methods, some of which like finishing were also used with the free-blown methods noted above.

To quote from Munsey once again, the following is additional molding specific information that notes the additional steps necessary in addition to the bottle blowing description noted in the free-blown section above the following would be the fourth paragraph in the Munsey excerpt above :. If the bottle is to be blown in a mold, the gaffer receives the blowpipe with the gather on it from the servitor and stands in position over the specific mold to be used. He then lowers the parison into the open mold.

If the mold is other than a dip or one-piece mold an apprentice will assist by opening and closing the parts of the mold at appropriate times. After the parison has been lowered into the mold, the gaffer blows steadily into the blowpipe until he feels resistance which signals him that the hot glass has assumed completely the shape of the mold.

He immediately ceases blowing and after the mold is opened he removes the bottle from the mold, ready for finishing Munsey Click molding a mouth-blown bottle to see an illustration of the described process.

One of the more concise descriptions of the operation and work allocation within a typical late 19th to early 20th century glass blowing "shop" producing mouth-blown molded bottles is found in the book Machinery and Labor Barnett The manufacture of bottles and jars by the method of mold blowing is carried on by working units known as "shops.

Two of the men blow and the third finishes. The blower takes a lump of glass from the pot or tank on his pipe, rolls and partially blows it. The mold tender, a boy, opens an iron mold and the blower lowers the glass into the mold. The mold having been closed, the blower inflates the glass to fill the mold. The pipe is cracked off from the bottle or jar, which is then carried by another boy - known as the "snapping-up boy" - to the finisher, who shapes with tools the neck and lip of the bottle.

The third boy - the "carrying-in boy" - carries the ware to the annealing lehr. A "cleaning-off boy" cleans the blow pipes of the blowers in preparation for re-use. Variations in this arrangement are found. In making some kinds of bottles, for example, a gathering boy gathers the glass for the blower, but the rules of the union have severely restricted this form of the division of labor except on very heavy ware.

Barnett The number of people involved in the organization of a "shop" was variable. The great image to the above right is from a West Virginia glass factory and shows a gaffer blower at work to the far left with his crew. This was also another typical mouth-blown shop crew working at the mold itself and included the mold tender boy lower right with a set of "tongs" in his right hand, the gatherer behind gaffer with the next gob of glass for the gaffer on a second blowpipe, and the "snapper up" to the right standing with a snap case tool in his left hand Lewis Hine photo, Library of Congress.

This crew may have also included one or all of the other workers noted in the above description finishers, carrying-in boy, cleaning-off boy but were not included in the image. The caption to the photo is: "Glass Blower and Mold Boy. Day shift one week: night shift next.

Grafton, W. The following link is to an amazing early 20th century film clip of a mouth-blown "shop" blowing bottles. It shows two gaffers and one mold boy in smooth and efficient action. The gaffer quickly inflates the bottle and efficiently bursts off the blowpipe while pulling the blowpipe away from the mold this is very interesting to observe and shows that shearing or cracking off wasn't always used or necessary.

The second gaffer is doing all of this on a staggered timing sequence with the first gaffer which allows the team "shop" to produce a bottle about every 20 seconds! Film clip is compliments of the Owens-Illinois Glass Company.

Many thanks to Phil Perry, engineer with that company. Early 20th century mouth-blown bottle making film clip. The following is a loosely organized collection of information designed to orient a user in the various methods and equipment used for producing mouth-blown molded bottles. Most of the information found here is an abbreviated version of what is found in more detailed form on other pages; links to those pages are provided in each of the subsections.

Bottle Molds. The large majority of bottles produced within the time span covered by this website early s to the midth century were produced in some type of metal mold e.

One source noted that the changeover from cut brass molds to cast iron molds occurred in England - and likely in the U. Molds could range from the most simple - a dip mold which could just be a bucket or dug out hole in the floor of the glassworks illustrated below on an old trade card - to the elaborate full sized molds with as many as 9 different mold sections Toulouse b. Molds increased the production of bottles greatly since less skills and labor were needed to produce a bottle with a mold than for a free-blown bottle.

While forming the shape of the bottle, molds leave behind diagnostic "bread crumbs" that provide information on the manufacturing techniques used which often allow help facilitate age estimating of a bottle produced Kendrick ; Munsey An example of a "two-piece" iron mold from a glassmakers catalog is shown to the left. Dip molds : The dip mold is a step up technologically from simple hand tool and marver manipulated free-blowing in the manufacture of bottles and was used for various types of glass manufacturing back into antiquity, beginning long before the era covered by this website.

A dip mold is a simple open top mold that was used to gain uniformity and consistency and likely increased production in the shaping of the bottle body and base. A simple one-piece round bottle dip mold is illustrated to the right showing its open top and the slight narrowing taper from top to bottom necessary for the removal of the inflated bottle Toulouse b.

Click modern art glass dip molds to see examples of such which - though not used for bottle production - are identical in form and function to those used for bottles in the 19th century and before. Photo courtesy of Bill Lockhart. Some dip molds were simply appropriately shaped holes dug into the floor of the glassworks Kendrick Dip molds were also used for shapes other than round, e. A square dip molded bottle is pictured below right. One-piece round dip molds would leave no classic raised mold seams on the body of the bottle more below.

Two or more piece, shoulder height, round dip molds could potentially leave fitting joint induced vertical mold seams on the body of the bottle, though this was likely uncommon. Multi-sided dip mold bottles may likely have been made from multi-part dip molds, though side seams showing the interface between the mold pieces are rarely seen, being either masked by the corner edges of the bottle or the bottle body was fire polished to the point that seams are unrecognizable.

Dip molds were made of a variety of materials including wood and harder materials like various metals, clay, and clay lined wood. One piece clay molds were particularly common during the early days of American bottle making Atwater Wooden dip molds - another common preth 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.

In use, the parison of glass on the end of the blowpipe is placed into the open top of the dip mold then blown and expanded to form the body of the bottle and giving the base at least its diameter and sometimes shape.

One-piece dip molds could produce about any cross section bottle shape - round, square, octagonal - but had to be designed to be removed from the top i. Two or more piece dip molds could theoretically have about any body shape or even embossing since the expanded bottle could be removed by opening the mold segments. Though a dip mold could be made of multiple sections, according to Jones they were not designed to be open and shut.

Apparently, dip mold bottles were not body embossed and even base embossing is uncommon but not unknown discussed below. Once the body and base were fully expanded within the mold, the bottle was removed and the shoulder and neck formed to shape with glassblower skills and hand tools like a free-blown bottle.

The body of a round dip mold bottle will be very similar in appearance to a free-blown bottle except that a dip molded bottle will tend to be more symmetrical in shape with little or no distortion.

This includes the general lack of the flaring of the extreme lower body and heel that free-blown bottles will often but not always have. Click free-blown lower body to view a picture showing base flaring on an early to midth century free-blown bottle. The body of a dip molded bottle will not have embossing. Because of the surface contact with the mold the sides of a dip molded bottle body from the shoulder to the heel usually have some distinctly "ruffled" or vaguely textured look to it as compared to the glossy smooth, fire-polished surface of the shoulder and neck.

This type of surface glass discontinuity is a diagnostic feature of dip molded bottles, though it is not always obvious or apparent Toulouse b; Jones Another method to often differentiate a dip molded bottle from a similar free-blown bottle is to look at the junction between the body and shoulder.

Dip molded bottles will very often have a distinct discontinuity in the glass appearance right at the break between the the body and shoulder due to the "blow-over" effect induced by the mold ending at that point; i.

This shoulder discontinuity could also be considered as a type of mold seam, though not with the typical look of regular mold seams where two parts of a mold come together Shafer ; Jones ; Deiss pers. This shoulder discontinuity is easier to see than describe and is shown distinctly in the picture at the following link - dip mold bottle shoulder - which is a close-up of the bottle to the left.

This is a dip molded ale or liquor bottle with a glass-tipped pontil scar that dates from the s. The picture also shows the glass surface texture difference between the body slightly wavy or rough and the shoulder smooth and glossy.

This shoulder mold seam or discontinuity can be observed on any shape of bottle that could be dip molded, though on square bottles it is not usually as obvious as on a round bottle empirical observations.

The square, dark olive green bottle to the right is a dip-molded "case" or "tapered" gin that dates from the midth century Shafer This particular bottle was produced near the end of the dip mold era as it is not pontil scarred and was found in western Oregon in the context of post-Civil War era items.

It is possibly American made, though that is impossible to say for sure. The body of this bottle was dip molded in a square mold and has a faintly embossed cross on the base of the bottle - sure proof of molding. Click base embossed cross to view a picture of the embossing. Base embossed dip molded bottles are unusual though obviously occurring. Click case gin shoulder close-up to view a close-up picture of the interface between the crudely dip molded sides and the "free-blown" shoulder.