Molds - Wood, Clay & Metal

Rev. ... 2003-03-06, -04-04, -06-24
2004-09-19, 2005-02-05, -02-09, -04-18, -11-11, 2006-11-11, 2007-05-26, 2008-03-27

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Molds used in art and production glass work fall in four major categories: optics, blow molds, press molds, and special tools.  This page on the history of bottle making has excellent examples of molds and their results and includes a short video of hand blown bottle making Glassmaking and Glassmakers Page 2007-05-26

Optic molds (or optics) are metal open ended tube molds that form ridges in the outside of the glass.  These ridges may be straight lines or diamond patterns, etc.  Most optic molds are solid, but those with complex patterns require a hinged split to remove the glass. Jim Moore makes a blade optic in which metal strips in a frame make the grooves. Homemade cast optic below right and rod optic below left. The primary variations in optic molds are: whether the bottom is open - usually meaning straight sided to the mold - or closed - usually meaning the pattern curves from the sides to the bottom, impressing the end of the glass;  the number and deepness of the grooves in simple patterns; size; and the design of alternate shapes. A straight groove optic can be used to hold and apply straight stringer.  Steinert is a primary purveyor of open optics.

Blow molds are a major factor in production glass and can be used in speeding steps in off-hand glass. Common terms are dip mold, turn mold and pattern mold.  In the dip mold the hot glass bubble is inserted, inflated, and withdrawn, thus being suitable for optics or square or triangular prisms.  A turn mold being where the blower rotates the piece in the mold to eliminate mold lines where the halves come together.  A pattern mold, perhaps also described by the number of parts coming together - 2 piece, 3 piece - has specific shapes inside the mold - a flask bottle with wide and narrow sides with an image of a person or building on the wide side..  Molds may be made of wood, usually fruit wood, soaked in water, or of metal, traditionally cast iron but more recently aluminum. Metal molds are treated inside with a baked on paste, for example resin or linseed oil and cork, that makes the surface more like a burned wood surface.  Blow and press molds must be preheated for the best detail.  This is usually done by simply making a couple of throw away pieces with hot glass so the mold gets up to several hundred degrees.  Glass will stick to a mold that gets too hot. 2004-09-19  The simple mold at right is just a steel conduit tube with a welded on bottom, drilled for venting and lined with a cork sheet (and disk at bottom) that is soaked wet before use.  I built it to make small cylinders of art glass to cut open and flatten for painting and fusing compatible with the blown glass.  2005-04-22

Blow molds are used by placing the blower above the mold, often on a box or a couple of steps up, with the pipe hanging straight down and the hot glass sagging below that. Because some, though not all, molds have restricted tops to make a neck, and because molds may be impressing a design into the glass, molds commonly come apart into several pieces and may hinge off a base or on the side.  Blow molds may be turn molds, for a radially symmetrical shape, which are the topic discussed below, or fixed, often 3 part molds, for impressed designs. Molds may be wood, metal, or graphite.

Press molds are used to make pressed glass and are open faced with a matching plug that drives the blob of glass into the mold, also forming the inside of shape. Pressed glass must taper inside to let the plunger out.  To allow removal of the glass, multipart exterior molds are used, leaving slight seam lines.

Special tools may be molds, such as those used to form the necks of bottles. Jim Moore is offering sheet metal fin molds that give a 6 or 8 sided form to the bowl of a goblet when pushed inside the soft glass bowl. 2003-06-24

The mold at the right is used by Brad Abrams and was originally cast and built by Steinert then rebuilt locally after a fire. As mentioned above, the blower stands on the platform left and pushes the button on the valve next to the white wood to close the mold through the manifold at the upper right, inflating the glass inside the mold. Lacking dual tubing for double acting and exposed springs, I would guess the recovery springs are internal to the cylinders.  The piece made is shown in the insert and is an enlargement of a dradle, normally a small child's Hanukah toy with a shaft on top for spinning on the point - with one Hebrew letter on each side.  Besides selling it as an ornament, with a pressed glass base that fits the point, it is sold as a oil candle.  Brad is exploring other uses for similar but more flexible equipment.   2005-02-05

The turn molds at the right are 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. The Czech blower at the GAS03 Conference used beam clamps on the square wooden molds for handles (Walters are turned round.) 2003-06-24

An iron mold is lined with pitch and powdered cork, baked into place, and the mold is also wetted down to soak the lining. Most iron molds, because of the expense, are made for production and have lugs to permit mounting on a device so the blower can open and close the mold with foot pressure and raise and lower the mold in the water. While aluminum has a melting point (1330F) far below that of glass, if the aluminum is thick and lined, it can be used as the heat will be sucked off before the aluminum mass reaches the melting point.

There are dozens of variations on molds, the most widely known in the historical glass business being three part metal molds used around the beginning of the 19th century. Because of their expense, they were reused for years and used as the basis for multiple glass objects, so the same glass mold design may be found in a pitcher, a decanter and a large bottle.

Jim Moore is now selling metal "blocks" that are thin cast shells with a cork lining.  The material is aluminum per his catalog. [2003-06-24]  They are being shown on Olympic Color Rods site, 1" to 10" $40-$60 2002-09-15

The following is a discussion originally posted on the Craftweb Hot Glass site, edited and copied here with permission of the authors.

Re: cast iron blow molds

Re: cast iron blow molds
Posted By: Ed <keithorr@aol.com> *permission to quote below
Date: Friday, 15 February 2002, at 3:08 p.m.

In Response To: cast iron blow molds (Jim)

: I have an old cast iron blow mold for a 16 oz tumbler and would like to
: experiment with it. Does anyone have experience they could share on mold
: preparation and/or tips on general technique?

The subject can take a lot of space on a message board. I have blown cast iron and graphite paste molds for over 20 years in production. If you have any specific questions, you are welcome to contact me by email.

In short, (ha), if it is a basic turning mold (you turn the pipe while blowing) you will prepare the mold by removing the old paste. (Paste is the coating of resin and cork.) You can use a torch to burn off the old coating. Get to clean metal. Prep the cast iron surface by rusting the clean metal. Use salt dissolved in warm water and dip the mold. Dry and repeat as required until there is a thin layer of rust. Wipe out the mold with a rag to remove any rust dust. This will help the first layer of paste bite into the surface and not delaminate later in production.

For the first layer, warm the mold in a kiln to 425F. Brush on a thin layer of Renite MP. The Renite will smoke and dry leaving a gummy glaze. When the mold has cooled to the temp when spit doesn't sizzle, brush on another layer of Renite MP. Use cheap natural bristle brushes, 1" wide. Throw them out when done with the mold. This layer should have some build to it, but not leaving puddles. Pull the material over the surface with the brush until the resin is even and glossy. Pour granulated cork onto the open mold. Dump out whatever doesn't stick to the resin. The cork blows around so make sure the container of Renite MP and the brush is covered. Pour more cork into the mold just to see if any more will stick. Dump out and lightly blow out the mold with breath or compressed air to remove any loose cork. Bake the mold for 90 minutes in a vented kiln. A gas fired kiln under a hood is best. There will be fumes. It stinks. The baking will dry the resin, but shouldn't burn the cork. The cork should be spongy after baking. If you determine that the cork is burnt, (dark and crispy), lower the temp. If the mold is gummy or resin sticks to your fingers when the mold has cooled, increase time.

Repeat the process to add a second layer. The difference between the first and second coating is that you pre heat the mold only to the temp required to get the resin to flow. Re: flow, The resin is thick in the bucket and the warm mold melts the resin allowing you to brush on a thin layer. Make sure the resin is not too thick. The first layer of cork will absorb resin and you may have too much. Daub the mold with tissue to remove any excess resin. At this point, the cork should be coated, but you should see the texture of the cork. You don't want a lot of resin between the grains of cork. Coat with cork like the first time. Bake 90 minutes.

After the second baking and the mold has cooled, lay the mold open face on a work surface, not a marver. Spray the mold lightly with water and rub a gob of molten glass over the surface, top to bottom, not side to side. (Against the direction you will be turning when you use the mold for blowing) The temp of the gob shouldn't be too hot or you'll stick it to the paste. Use a light touch and try to glide the gob over the surface. This process knocks down the surface and smoothes the paste for the final coating.

Apply a third coating like the second. Let the mold cool.

Again, knock down the surface with a hot gob of glass. If you've done it right, the mold is now ready for use. For a tumbler mold, the paste should be good for two thousand pieces or so.

A mechanical mold boy is best. But this is another subject.

In identifying problems, if after cooking a layer of paste, you see blisters in the paste, it means you used too much resin. If the cork is dark and hard, the temp was too high. If a lot of "grease" bleeds from the mold when blowing, you need more cooking time.

The value of production molds is to reduce the time required to make a piece. If you are pre-shaping and necking and making everything pretty and then using the mold for a final shaping just to perfect the shape, then you are a turd and should be shot. To use a mold effectively, you should be going in hot and loose. The mold is wet, the glass is soft, the water held by the paste will turn to steam and make a cushion leaving a smooth surface. Blowing cold can leave a worse finish than hot because you blow with more pressure and blow through the steam layer and contact the paste too hard, but the mold must be prepared properly for hot blowing to work. I make graphite molds for paste and can paste the mold the first time for a customer, but your mold is already in your possession, so all I can say is good luck.

Ed Skeels

Renite
Posted By: Ed <keithorr@aol.com>
Date: Friday, 15 February 2002, at 9:41 p.m.

Renite ( www.renite.com ) sells mold paste in huge one gallon buckets. Should add that you can use sawdust instead of cork, but the dust doesn't build the surface up as evenly, and doesn't have the porosity to hold water. If you use sawdust, don't use plywood, particle or chip board. Take some old cherry wood blocks or paddles and run them through a table saw. I only know of one cork company and the minimum is a bag big enough to fill a 30 gallon garbage can, which can last the lifetime of most studios. Many mesh sizes available which is a hassle cause they don't know what you are doing with it. (They don't blow glass and can't suggest a size for you). If you need some I can bag some in a big ziploc and send it for $$$. I have two mesh sizes, one for small molds that need a fine finish, like goblet molds, and a larger mesh size which makes a thicker build to hold more water on large shapes, like lampshades.

Re: Renite temp
Posted By: Ed <keithorr@aol.com>
Date: Saturday, 16 February 2002, at 4:16 p.m.

In Response To: Re: Renite (Jim)

Renite can send instructions with the mold paste. I think they suggest 475F (or abouts) for 90 minutes. Like baking a cake, just put it in. I found 475 was too hot and cooked the cork. Could be my thermocouple placement. The cork should come out of the firing looking only slightly darker than when it went in. If it's overcooked, it doesn't burn back smoothly when used for blowing and leaves zillions of lines in the vessel. Like blowing on 80 grit sandpaper. Your cooking temps may vary.

Oh all right.

Ed

Posted By: alex <bigshot@glassattack.com>
Date: Saturday, 16 February 2002, at 3:01 p.m.
In Response To: Re: Cast iron- the source question (Pete VanderLaan- faux moderator)
Those looking for a cast iron blow mold source, try: www.lynchindustry.com/glassware.htm

Alex
Posted By: F.Thumb <dan@flamingthumb.com>
Date: Saturday, 16 February 2002, at 3:03 p.m.
This is where I got my cast iron molds made at (it was a referral from Walter):
West Virginia Mold Shop Paul 304-269-4436

Posted By: F.Thumb <dan@flamingthumb.com>
Date: Saturday, 16 February 2002, at 2:59 p.m.
I don't know if they are still doing this, but several years ago I called Maryland Cork Company (410-398-2955) and asked for some samples of cork dust. They sent me (free) four 1 lb baggies full of cork powder. I'll have to get the pictures of my mechanical boy to post now. Haven't used it yet, but still mean to as soon as I've got our new/improved studio finished. Thanks for all the info on set up.
- Thumb
Re: Cast iron- the source question
Posted By: Ed <keithorr@aol.com>
Date: Saturday, 16 February 2002, at 3:51 p.m.

When I said pre-shape, I was thinking about a conversation with Walter. He was talking about the class he gave at Corning, and how the students dressed the shapes before blowing. Kind of defeated the purpose of molds. When you see production blowers slinging glass into molds, it looks "easy," but when it's your turn, you soon realize the level of comprehension required to make the leap of faith from safe, cold and slow, to slamming goo. I can remember for myself, the time it took and still takes with some new shapes, to make the transition from caution to comprehension. Shapes that used to take 15 minutes of prep to get to the mold now take five. Learning what corners can be cut and still get the glass to flow in the mold so the thickness and applied design ends up where you want is a process. But tumblers, come on, that's so stupid.

West Virginia Mold Shop. (304) 269-4436. Know what you want before you call. They don't hold hands. They offer molds for handblown as well as nickel molds for automatic mold blowing (bottles). From what I remember, they keep billets of aluminum in stock that they can CNC goblet size shapes. The guy said, "About the size of a coke can." They can cast aluminum or I think cast iron for larger shapes. Cost gets high pretty quick on the cast shapes, so machining from billets of metal or graphite is more economical. They aren't really into the onezy twozy thing. They considered taking over the demand from Walter but balked at all the hassle of getting lumber and storing it. Plus dealing with studio blowers unfamiliar with the process. Just no money in wood unless you charge prices approaching graphite.

Another source is Island Mold (304) 233-3970. Tried wood a couple of times for customers but quit. Same hassles. Metal molds for production. Same as above. Had phone manners approaching mine so I didn't get too far with them when seeking information.

The lighting company who endures my psyche placed a CNC mill in my shop so I can make shapes for their work. I make the lease payments and they buy any molds I make for them, plus I can use it for myself. Nice for titanium "go away" signs. I have milled molds to 18" high by 14" diameter. The graphite rod for a mold this big was about $1500. Machine time was several days. I am getting good at the programming now and can go from a scanned drawing to a 12-20 inch high milled mold 6" dia. with hinges in about a day. Pasting takes another day.

Aluminum can be cast or spun for molds. The spun molds would be open top with no undercuts or hinges. Like blowing into a wastepaper basket. You need to be able to drift the piece up and out after the shape sets. The setup for blowing this way is different from blowing a mold with a neck, because the "hat" on top doesn't contact any metal, but has to cool enough to support the shape. Refer to Essemce mold boys with cooling lines. After the shape sets, you step on another pedal and cool the hat with compressed air.

Aluminum molds paste fine, temp limits on some alloys are a problem, so lower temp, more time works well. Note that the Renite paste or double boiled linseed oil will reduce to tar at room temperature in a couple or weeks. You don't need to achieve any specific temp when cooking, its just a matter of practicality. Pushing the limits reduces the time.

One thing with aluminum is that you can't put the mold into a 900F lehr to burn off the old paste like you can with iron. The Renite product bites the surface pretty good. Sandblasting helps a lot. The trick is to put on the first layer when the mold is hot enough to smoke the resin. This first thin pre-layer is really a tacky varnish that holds the first layer of resin and cork. Putting the first layer on a warm mold without this layer of varnish just doesn't hold as well.

One advantage of graphite is the paste cooks more evenly. Graphite is a great conductor of heat. The problem with iron molds is that the mass of metal takes too long to achieve an even temperature throughout the mold. Areas where the metal is thicker takes longer to cook. Thin sections overcook, so you can have a zone in the mold where the paste is sliding across the surface, while other areas are cooked hard.

Another solution to paste is a machined graphite mold that is doped with boron. The finish must be kept immaculate. Any shop grit or flakes of graphite from the edges of the mold leave bad lines, so not that good for high finish wares. Great for static blow molds. Raw graphite leaves little cracks on the glass, unless you buy the expensive grades. Can also spray graphite compounds on the graphite mold to eliminate checking (cracks). Renite AKX for foundation and S-24 top coat. Ed

Ed Skeels
Guardian Angel

Registered: Apr 2002
Location: Napa, California
Posts: 65
A little knowledge isn't always dangerous, but like glass recipies, worthless.
"We have tried it, and have met with limited success. We think it needs to be re-pasted"
I've been mold blowing exclusively for almost 25 years, and I take certain things for granted. I have recently come to the notion that molds are kinda technical, and can't be learned in a week.
The best paste I've found has been on used molds. Practice makes perfect, and factory molds benefit from being used and prepared by experienced hands.
If there is paste on the mold, it's probably fine. If there are chunks missing, then it might be time to redo it.
I would suggest washing the mold with soap and water using a soft paint brush, to remove any loose bits, then rinsing well. Then I might consider sanding the surface of the paste. I say might, not would. There is no way to tell via phone or internet what is necessary.
If the user isn't practiced in mold blowing, I would be more suspect of the blower than the mold. Since the writer doesn't know what kind of cork to get, and doesn't indicate experience with the paste process, I can only assume the problem is not in the mold. The ability to work freehand does not infer proficiency in moldblowing. Watching offhand blowers try to adapt their understanding of glassmaking to molds is either funny or pathetic, depending on the mood of the viewer.
Eben writes in another thread about the meaning of words used to describe a melt, and the confusion therein. Hands on learning is different from reading Scholes or the GAS transcripts. Words can spark the imagination, but transference of knowledge is best done in person. If someone really wants to know how to blow a certain shape, or paste a mold, they can come to my shop and pay money.
The mold paste page can no longer be accessed from my webpage. I have removed it as I consider it useless primer.
I will be at Blenko on Tuesday to deliver some molds. I'll try to get some video. Their work is rough, but they know how to hump glass and fill a lehr.
 

Clay Molds
I have been working on a flip apart mount for a 3 piece mold for some time to make a 3 sided bottle or a log candle holder.  I came across a Penland Ceramics books which gave detailed information on slab building.  Using my old faithful white clay I decided to build some test pieces. 
 I cut outline patterns of the sides and bottom from stiff cardboard illustration board for 6x3 inch forms in 3 ways: no taper, 1/8" taper and 1/4" taper.  These two are the 1/8" and no taper models. [1/8" is off vertical, so the bottom is 1/4" narrower than the top.] The picture shows more distortion than exists in the pieces and the tops were trimmed after taking it.
 The clay was roughly cut from the 25# block with a wire cutter and then rolled with a rolling pin that takes rings for specific thicknesses, 3/8" in this case.  Lacking a special pin, an ordinary cylindrical rolling pin held up with thin slabs of wood with the clay in between them.  The book says he prefers to cut to exact thickness with the wire held on rods with nails at the spacing he uses, because he feels rolled slabs are more likely to warp, but I felt 3/8" was very thin to cut to thickness.  After rolling, the cardboard was used to guide the knife to cut a 45° bevel.
  The slabs were laid on several layers of newspaper to firm up to leather hard, which takes about 10 hours.  When stiff enough to handle, the edges were grooved with a fork and slip was applied with a brush. (Slip is just clay dissolved in water to make a thick cream - it takes a while to get all the lumps out.)  Two sides were lined up and joined and then set on the base.  Then the other sides were added.  If this were a pot, the joint should be reinforced on the inside and the outside worked smooth, but I am making a mold, so a lot more attention was paid to the inside (not shown), getting pinching closed joints, adding slip to smooth, straight lines, etc.  After the clay had firmed up some more, a drill was used to place vent holes (visible in the photo) on all four sides and the bottom.  Now to let it dry and fire it in the annealer and glory hole. 2005-02-09
  After some quavering, I decided to go ahead and make a neck mold for the top, trickier clay work.  Making it separately means I can use these, if they work, as an insert mold and try the neck separately. 2005-02-09

A very busy day yesterday.  Tried again to do an aluminum sand cast, melting in gloryhole (below) failed. Memo: make mold before melting, don't rush.  In the back of the gloryhole fired ceramic clay molds, raising temp after removing aluminum, (lower right) okay, but molds fell apart or cracked at joints. Taken out hot. Poured wax for yet another optic casting, this time with support pins.  Blew glass in molds and otherwise - see below.  2005-02-15

Well, I did an experimental session and partly succeeded and mostly failed.  To the right is the glass from the mold below.  The mold cracked at the corners (lower right) and the piece was not properly reheated out of the mold and cracked all over the place while working, but I was able to keep it together for the best image.  The far corner visible right through the opening is actually broken open and other cracks circle the bottom and halfway up the flat sides.  2005-02-15
The original mold construction plan was built around square bottles and the one at right was blown from the mold lower right.  The bottle has a crack across the bottom and up the sides from the punty mark.  Of the two molds shown above, the tapered one came apart in the kiln during cool down, below, and the other popped its bottom while blowing.  2005-02-15
Below are the three molds from above after gluing them with E-6000.  The wiring harness is backup security.  Considering what took to take apart glass and metal with E-6000 (850°F not 650°F)  2005-02-15

The next step is to make a split mold with an attempt to make something as quick as possible.  When I used the example of a golf trophy in explaining what I was trying to do, I decided to make one.  I decided a bottle 3" on a side would fit my hand nicely.  I cut 6x6" poster board and grooved it to fold 1-1/2" on each side, taping to hold the fold. [bottom row]  On one side, I imbedded a golf ball part way through a cardboard mount.  I added clay slip to be sure the clay got into the dimples on the ball.  I should have oiled or greased the ball as easing it out took some time.  On the other side, I molded the head and lower shaft of a golf iron from Plasticine clay. Here I painted slip in the grooves to be sure they were defined.  In both cases I rolled the grey potters clay to 3/8" thick, cut it to 6"x6" and forced the very soft clay down over the cardboard and molded it around the decorations, working out the bubbles.  The ball wanted to push back through, so I added a lump of clay to support it.  I also rolled a base 4x4" and sliced a curved line through it to align them.
After letting the clay start to dry (approaching leather hard), I worked it off the mounts and carefully aligned the sides to let it harden.  The plastic clay iron came off the mount in the clay. [row 3, right]  Getting the plastic clay out became a challenge because both clays are soft.  I removed most of green plastic clay and then started heating the molds.  I expected the green clay to drip out, but instead it dried and cracked and crumbled when the temp was 210, so was easy to remove.  Doing a web search, the plastic clay used in claymation melts at 150F, but the recipes given for making your own oil clay are wax, grease, and oil with clay or talc (here) and with this much clay, melting won't happen. As I write this, the clay is doing a first heating/firing up to 900F over 3 hours.  2005-04-15  The images in the bottom row on the right show the mold after the firing.  The drilled vent holes are barely visible in the center of the ball and in the heel and toe of the club. 2005-04-18

 I built this press (instead of something involving welding and air cylinders) because of cheapness, materials on hand and incredible frustration that I could not blow glass for a long period.  [These pictures were taken 2005-09-23, look at the dates above and finally blowing glass into them below]  This montage shows the open and closed positions.  The wires on the clay mold insure they are pulled back.  The cutaway on the vertical support clears the protrusion off the ball/club head on the mold. The metal angle at the left end is a step-on to open while the raised section is step-on to close.  The left end wood is screwed down, the right end is held by screws with washers through slots to accommodate different molds.  The only thing I would add is a pair of guides midpoint on the slider (about where the picture seam is) to keep it from slipping sideways. Big, awkward, easy to build, easy to use. 2005-11-11

I blew into these molds and recovered a glass piece (below) that shows all the problems of blowing square and into deep set molds - cracked all over the place and lost one in the glory hole.  The bottom popped off also.  Inclined, in this case, to use a flat plate all the way across the bottom instead of trying to make matching half plates and firmly attach them. The mold of the club head, which was originally made in clay came out with better definition that the golf bowl, which was a real golf ball pushed through a hole in cardboard.  No real dimples at all.  Probably protrudes too far but maybe okay with more practice. 2005-11-11

I have had some clay faces around that I have gradually worked on to improve their looks and I decided to mold this one off and impress it in the clay as above.  This time, I made a wax impression (not shown) to melt out of the back of the clay.  Shown are the latex negative and in investment positive to be used in making a stamp beside the clay shape like the golf club above - the face was put on the same cardboard and again slip was painted into the details before the soft clay was pushed down on the positive. 2005-05-01

Other Techniques
This site [Roman Glassmakers Articles Page] has explored techniques in Roman Period Glass and says this on a page that discusses other techniques and problems "The most obvious point to note is that the mould has to taper very slightly outwards towards the top (a millimetre will do). If it doesn't, the bottle will not come out of the mould.
If using a sandstone or terracotta mould - as the Roman glass-makers did - it is important to keep it slightly damp. If it is dry the molten glass can adhere to it, particularly as it warms up, resulting in small pieces of sandstone sticking to the bottle. The base is especially prone to this as it is in contact with the part of the parison which is at the highest temperature, and it will result in the loss of the carved detail.
If the mould is too damp, then cooling rings can appear on the walls of the bottle." These people use plain sides and a patterned bottom plate.  They also say that for their reproduction work, they use kiln shelves which they texture like the sandstone, but which last much longer.  2005-11-11

Sheet Metal Molds Stainless sheet metal can be used for dip molds, by folding the sheet to make a deep "cookie cutter" pattern or by making sides and clamping at the corners.  The picture shows 3 curved sheets with flange bent back at angle to provide clamping surface while holding the angle of the design. For scale, the clamps are 1" between jaws 2008-03-27

Contact Mike Firth