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Hemispherical Half Dome Molds


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I'm looking for half dome hump molds to make poppy heads. I'm looking for a least cost, least time expenditure way to acquire them.

I've found a steel company that stamps them in different sizes and they're cheaper than any other supplier of that shape in any other material.

I have a feeling metal might not be the best material as it may be sticky enough to cause shrinkage and removal problems. But, I don't know this to be a fact so have any of you used molds made of steel?

If so are there tips and tricks to molding clay against metal? Are lubricants required, etc.?

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It will definitely stick, and depending on the grade of steel there may be problems with rust. Anything non-absorbent like that you’ll have to use some kind of mould release with, whether it’s something like cornstarch, some form of lubricant, or a physical barrier like thin plastic or cloth. Any time you’re using a hump mould of any material, you do have to time your removal properly because if the clay is shrinking around a rigid item, it can crack. 

What level of production are you looking at? It can be worth it to take a day and make your own out of bisque or plaster if you only need a handful.

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I don't do anything in production. I do this because I like doing it. Total poppy heads? Maybe 10 or 15. If they sold I might make some more but I'll probably get distracted by something else by then. :-) I'd use them as drape molds and the interior surface of a poppy head is no concern. 

Drying while on the mold would be short term as I'll need to connect the two halves, add the leaves and the ribs so they all shrink together at the same rate.

Would PAM cook off in the kiln?

I could throw some and bisque them I guess.

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a visual would sure be good here.   yes, there is a studio in florida which uses Pam and all kinds of materials to form pieces.   i use WD40 and have since the 1990s.   i hate pam's greasiness and other people do not like the smell of WD40.   if there is a dollar tree near you, you may find plastic christmas tree ornament sized balls.   i have used several to form spherical bowls using upholstery foam.  

are you aiming for an entire sphere?  ribs?? leaves?  photo, drawing would explain what you are looking for.

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Looking to build spheres; different sizes, ~4" to 8" to which I'll add the top leaves and ribs.

I'm looking for a least cost, least time expenditure way to acquire something like this to use as a drape  mold.

Screen Shot 2021-07-06 at 12.47.25 PM.png

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Posted (edited)
1 hour ago, Magnolia Mud Research said:

switch from "hump" molds to "slump" molds; thin use the half-dome steel forms; the clay shrinkage will pull away from the form without cracking.  coat the form starch.  has worked for me using glass, metal, and "found object" forms. 
LT

Thanks for the tip. I deal with Clay King so was using their terminology. http://www.clay-king.com/pottery_wheels/hump_molds.html

Why would they be called 'slump' molds? Slumping is a term indicative of a negative, a fall, slouching, etc. The definition of hump would be more appropriate for these types of molds (something that's a positive aspect 'above' a surface, etc.).

Edited by ThruTraffic
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@ThruTraffic check your local budget/thrift/secondhand store.  I find things there for molds.  Also, do not count out wood.  For small things I have used wooden eggs (found at Easter)  I have a wooden bowl that I used to make a mold out of clay, then bisqued it.  I have used Pam and WD40 in the past.  Cornstarch is my friend currently to keep things from sticking.

Roberta

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1 hour ago, ThruTraffic said:

Thanks for the tip. I deal with Clay King so was using their terminology. http://www.clay-king.com/pottery_wheels/hump_molds.html

Why would they be called 'slump' molds? Slumping is a term indicative of a negative, a fall, slouching, etc. The definition of hump would be more appropriate for these types of molds (something that's a positive aspect 'above' a surface, etc.).

slump_hump.png.0ac92df4453e1dc42e8ad80d7c2a5b8e.png

^^^^ slump mould (clay on concave face)........^^^^ hump mould (clay on convex face)

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I'ld buy some cheap plastic balls then roll out a thickish slab of clay and drape it over the ball. Compress it, rib it well, remove from the form when stiff enough to hold its shape but don't leave it too long or it will crack,  when dry bisque fire it. Use that for your mold, no need for veg spray or WD40. You could use either the outside (hump mold) of the bisqued mold or the inside (slump mold). The bisqued mold will release the clay far faster than using a metal or plastic mold.

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8 hours ago, ThruTraffic said:

Why would they be called 'slump' molds? Slumping is a term indicative of a negative, a fall, slouching, etc.

just cuz "slump & hump" sounds so cool & simple, is my guess :rolleyes:  you are slumping the clay into the concave & humping it over the convex; I use light coconut oil on a cotton ball or cornstarch-so no sticking. I use all kinds of materials for half rounds (and other forms) & then bisque the clay molds-polished/smooth wood forms actually work well

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9 hours ago, LeeU said:

 

just cuz "slump & hump" sounds so cool & simple, is my guess :rolleyes:  you are slumping the clay into the concave & humping it over the convex; I use light coconut oil on a cotton ball or cornstarch-so no sticking. I use all kinds of materials for half rounds (and other forms) & then bisque the clay molds-polished/smooth wood forms actually work well

I'm humping.

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14 minutes ago, ThruTraffic said:

I'm humping.

That's your choice. but let's not let the discussion on terminology obscure MMR's point.

19 hours ago, Magnolia Mud Research said:

switch from "hump" molds to "slump" molds; thin use the half-dome steel forms; the clay shrinkage will pull away from the form without cracking.  coat the form starch.  has worked for me using glass, metal, and "found object" forms. 
LT

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As I craft forms from combined shapes I have many spheres in my studio. Acrylic tree ornaments come in a variety of sizes and mold easily.  Bowling balls make great models. (Mold easily, don't distort.) Most bowling alleys have one or two chipped balls in the back room. 8.5"  dia. exactly. You can also order "acrylic domes" from a variety of companies. (They're nice because they are seamless whereas the ornaments have a seam.)

In a quaint part of Minneapolis they have street lights with plastic sphere diffusers. I checked with the grounds crew and they had a 12" and 22" inch diffuser in the back room. (Both with cracks however.) Those have been invaluable when I wanted to mold a large sphere form. 

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I'm making about half my better pot  production using hump molds now.  Using Hot Wire Foam Factory products I custom make round and oval styrofoam hump molds in pretty much any size I want.  They can be finished with a cement like product from them or even hydrocal.  I cover the styrofoam mold with plastic food wrap before applying the clay slab.  It's so thin it doesn't leave any texture to the inside of the pot.   The mold then just lifts right out of the fresh wet pot.  Any touch up is easy at that point, you're not dealing with a leather or harder pot.   The nice thing about a hump mold is that the pot can be completely finished in one go, feet, rim, whatever.  Just depends on what you're trying to make, but for my purposes, I think this is ideal

pot 6 resize.jpg

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When I was in high school our pottery teacher would have us buy a styrofoam  ball or head,   We would build our clay work on it,  when it was firm enough, we would pour lacquer thinner on it and melt the styrofoam.   The problems the students would have was working to thin and waiting to long to melt it,  both problems cause major cracking.  You can make a round sphere by covering a balloon with plaster.  You could make the first half making sure to leave some notches so you can align it later.  When the first half is set up vasoline the edge and notches well,  place the plaster side down in the bowl that is supporting your balloon  and plaster the other side.   Denice

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Melted styrofoam, vasoline, or any other traditional release will leave some residue on the clay.  No big deal, unless you want to do any additional joinery. 

Seriously, the plastic wrap is the way to go.  It doesn't even have to be neat.  Even if there are a bunch of folds, there still isn't enough thickness to leave much of a mark.

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