Jump to content
  • Announcements

    • Jennifer Harnetty

      Moderators needed!   12/08/2017

      Ceramic Arts Network is looking for two new forum moderators for the Clay and Glaze Chemistry and Equipment Use and Repair sections of the Ceramic Arts Network Community Forum. We are looking for somebody who is an active participant (i.e. somebody who participates on a daily basis, or near daily) on the forum. Moderators must be willing to monitor the forum on a daily basis to remove spam, make sure members are adhering to the Forum Terms of Use, and make sure posts are in the appropriate categories. In addition to moderating their primary sections, Moderators must work as a team with other moderators to monitor the areas of the forum that do not have dedicated moderators (Educational Approaches and Resources, Aesthetic Approaches and Philosophy, etc.). Moderators must have a solid understanding of the area of the forum they are going to moderate (i.e. the Clay and Glaze Chemistry moderator must be somebody who mixes, tests, and has a decent understanding of materials). Moderators must be diplomatic communicators, be receptive to others’ ideas, and be able to see things from multiple perspectives. This is a volunteer position that comes with an honorary annual ICAN Gold membership. If you are interested, please send an email outlining your experience and qualifications to jharnetty@ceramics.org.
Sign in to follow this  
Strelnikov

Making a mold

Recommended Posts

I am trying to make my first mold and have made a wood box to surround the mold. I have some Murphy's Oil Soap to use as a release agent on the inner part of the mold. I was wondering if I could line my wood box with a black plastic garbage bag so the USG No 1 Pottery Plaster doesn't leak out of the wood box. I have read that the plaster heats up when it's curing. Will it get too hot and melt the plastic?

Share this post


Link to post
Share on other sites

If you clamp the box tight enough, it shouldn't be an issue. Otherwise, you could use coils/ wads of clay to act as a seal, on the inside corners.

 

 

Thanks, that would work but would take more time than just putting a black plastic garbage bag inside the box. Just wondering if anyone has tried that successfully.

Share this post


Link to post
Share on other sites

If you clamp the box tight enough, it shouldn't be an issue. Otherwise, you could use coils/ wads of clay to act as a seal, on the inside corners.

 

 

Thanks, that would work but would take more time than just putting a black plastic garbage bag inside the box. Just wondering if anyone has tried that successfully.

 

 

Can't say I have. In regards to your question about the heat, there have been cases of people being burned by plaster, especially when doing plaster wrappings of body parts. Though, some of that, I believe, has to do with the plaster reacting with the moisture in the skin.

Share this post


Link to post
Share on other sites

If you clamp the box tight enough, it shouldn't be an issue. Otherwise, you could use coils/ wads of clay to act as a seal, on the inside corners.

 

 

Thanks, that would work but would take more time than just putting a black plastic garbage bag inside the box. Just wondering if anyone has tried that successfully.

 

 

 

Yes you should have no problem using the bag. I have done it. It does make for a less professional looking mold though as it is hard to keep all the wrinkles out of the bag. T

Share this post


Link to post
Share on other sites

Yes you should have no problem using the bag. I have done it. It does make for a less professional looking mold though as it is hard to keep all the wrinkles out of the bag. T

 

 

Thanks Trina, at this point I don't care much what the outside of the mold looks like, just the inside. I'm most concerned about the plaster sticking to my wood box. I had to use glued pine for the bottom because it's wider than 11-1/4" so I couldn't use a piece of the 1 x 12 I used for the sides. The sides varnished up nice and smooth but for some reason the bottom pitted when I applied the varnish. Very strange but I won't use that stuff again. Although clay would work, a plastic garbage bag is sure faster and easier to solve the problem of sticking to the rough bottom.

Share this post


Link to post
Share on other sites

I agree with Trina. You mold will look nicer if you put coils of clay along all the edges, both inside and outside. Your plastic bag may catch on your mold and chip. I use the spray on Murphy's oil soap. Works great. Don't worry about the plaster heating up. Not hot enough to melt anything.

TJR.

Throw your clay away after use. It will be no good for making anything.

T.

Share this post


Link to post
Share on other sites

I agree with Trina. You mold will look nicer if you put coils of clay along all the edges, both inside and outside. Your plastic bag may catch on your mold and chip. I use the spray on Murphy's oil soap. Works great. Don't worry about the plaster heating up. Not hot enough to melt anything.

TJR.

Throw your clay away after use. It will be no good for making anything.

T.

 

 

 

Is your box an actual box? or a frame? You are still good with the bag either way just curious. T

Share this post


Link to post
Share on other sites

Are you using cottle boards? Having those around makes it easy to make molds and every time you use them they get better because of the Murphy's soap sinking in. A bead of clay to seal the cracks is better than a bag. Even if you don't seal it with clay and it leaks a little, properly mixed plaster will self seal after spreading out a bit. (Note the word "little" in previous sentence.) Avoiding air bubbles will probably be a bigger problem than any of your present concerns.

 

Jim

Share this post


Link to post
Share on other sites

As Jim says, if you get into making molds cottle boards are a great asset. I seal mine with urethane.

I have several sizes. They are great for preparing for casting molds.

 

I agree with Trina that the plastic bag could make wrinkles and be a bear to get the plastic free. You could spray

the box with WD 40. Thta's faster than the bag. Benzines suggestion for coils at the seams is standard procedure for frames. But your box sounds all inclusive.

 

Marcia

Share this post


Link to post
Share on other sites

I agree with Trina. You mold will look nicer if you put coils of clay along all the edges, both inside and outside. Your plastic bag may catch on your mold and chip. I use the spray on Murphy's oil soap. Works great. Don't worry about the plaster heating up. Not hot enough to melt anything.

TJR.

Throw your clay away after use. It will be no good for making anything.

T.

 

 

 

Is your box an actual box? or a frame? You are still good with the bag either way just curious. T

 

 

It's a wood box made from 1" pine held together with wood screws.

 

Not sure about the bag now. Since this is my first mold my biggest fear is having everything stick together and having to destroy my box to free the mold. I would like to make several molds using this box.

Share this post


Link to post
Share on other sites

Are you using cottle boards? Having those around makes it easy to make molds and every time you use them they get better because of the Murphy's soap sinking in. A bead of clay to seal the cracks is better than a bag. Even if you don't seal it with clay and it leaks a little, properly mixed plaster will self seal after spreading out a bit. (Note the word "little" in previous sentence.) Avoiding air bubbles will probably be a bigger problem than any of your present concerns.

 

Jim

 

 

Never heard of cottle boards before, just have a wood box.

Share this post


Link to post
Share on other sites

As Jim says, if you get into making molds coddle boards are a great asset. I seal mine with urethane.

I have several sizes. They are great for preparing for casting molds.

 

I agree with Trina that the plastic bag could make wrinkles and be a bear to get the plastic free. You could spray

the box with WD 40. Thta's faster than the bag. Benzines suggestion for coils at the seams is standard procedure for frames. But your box sounds all inclusive.

 

Marcia

 

 

I sealed the inside of the box with 3 coats of Minwax Indoor/Outdoor Helmsman Spar Urethane. I'm concerned that the box is not straight, that the top is slightly smaller than the base, making the mold impossible to get out without destroying the box. Maybe lining the box with clay would be the best after all, so I could make sure the box has the correct taper to allow the plaster to come out of the box.

 

WD 40 is one release agent I've seen referenced, but more people seem to use Murphy's Oil Soap.

Share this post


Link to post
Share on other sites

Are you using cottle boards? Having those around makes it easy to make molds and every time you use them they get better because of the Murphy's soap sinking in. A bead of clay to seal the cracks is better than a bag. Even if you don't seal it with clay and it leaks a little, properly mixed plaster will self seal after spreading out a bit. (Note the word "little" in previous sentence.) Avoiding air bubbles will probably be a bigger problem than any of your present concerns.

 

Jim

 

 

Never heard of cottle boards before, just have a wood box.

 

 

If you plan to make more than one mold, you should google cottle boards. Then google "do a barrel roll".

 

Jim

Marcia Selsor likes this

Share this post


Link to post
Share on other sites

Are you using cottle boards? Having those around makes it easy to make molds and every time you use them they get better because of the Murphy's soap sinking in. A bead of clay to seal the cracks is better than a bag. Even if you don't seal it with clay and it leaks a little, properly mixed plaster will self seal after spreading out a bit. (Note the word "little" in previous sentence.) Avoiding air bubbles will probably be a bigger problem than any of your present concerns.

 

Jim

 

 

Never heard of cottle boards before, just have a wood box.

 

 

If you plan to make more than one mold, you should google cottle boards. Then google "do a barrel roll".

 

Jim

 

 

thank you Jim I couldn't think of the word for cottle boards....brain spazm..T

Share this post


Link to post
Share on other sites

If you plan to make more than one mold, you should google cottle boards. Then google "do a barrel roll".

 

Jim

 

 

Will do thanks.

 

 

Found a couple of good videos on YouTube showing how to make and use cottle boards.

 

The barrel roll didn't work on my iPad but I saw a video showing it.

 

I thought you got sidetracked and were talking about airplanes and air shows.

Share this post


Link to post
Share on other sites

If you plan to make more than one mold, you should google cottle boards. Then google "do a barrel roll".

 

Jim

 

 

Will do thanks.

 

 

Found a couple of good videos on YouTube showing how to make and use cottle boards.

 

The barrel roll didn't work on my iPad but I saw a video showing it.

 

I thought you got sidetracked and were talking about airplanes and air shows.

 

 

Yeah, I was just joking about the barrel rolls. Sorta cool that Google has a sense of humor. I don't know what you're doing but if you plan to make more molds cottle boards are well worth the effort to make them. It is so easy to adjust them to so many different sizes. I have two sets. One is for small molds and the other is for large molds. Good luck.

 

Jim

Share this post


Link to post
Share on other sites

One thing to consider is that I made my box out of cheap pine that wasn't very straight. The video I watched on making cottle boards (from Ceramic Arts Daily) said to use oak or birch plywood. That stuff has to be pretty expensive comparatively if I even knew where to get it. Home Depot has oak boards but they are very expensive. I don't remember ever seeing oak or birch plywood there. I guess the good thing is that cottle boards are adjustable and once you bear the expense of making them, they can be used many times.

 

Another problem is that I don't have a suitable base to put the cottle boards on. In one video the instructor suggested using something like a formica counter base I believe. What are you folks using?

Share this post


Link to post
Share on other sites

One thing to consider is that I made my box out of cheap pine that wasn't very straight. The video I watched on making cottle boards (from Ceramic Arts Daily) said to use oak or birch plywood. That stuff has to be pretty expensive comparatively if I even knew where to get it. Home Depot has oak boards but they are very expensive. I don't remember ever seeing oak or birch plywood there. I guess the good thing is that cottle boards are adjustable and once you bear the expense of making them, they can be used many times.

 

Another problem is that I don't have a suitable base to put the cottle boards on. In one video the instructor suggested using something like a formica counter base I believe. What are you folks using?

 

No need to use oak or birch, just use plain old pine or any other inexpensive wood. Mine are pine and are nice and straight and have been used for years and only get better with age. Just use any wood that is straight and smooth. You can set them on any work table. I spray a little WD40 on the table first then use the cottle boards. If I want an especially smooth bottom to the mold I set my cottle boards on my grand piano.

 

Jim

Share this post


Link to post
Share on other sites

I use a piece of formica but any smooth wood like smooth plywood will work.

The mold will be nicer with clay coils smoothed into all corners-I did a photo post on this last two springs ago.

Mark

Share this post


Link to post
Share on other sites

I use a thin sheet of plexiglass. It gives a mirror smooth surface for the bottom and plaster won't stick to plexiglass.

I use the cottle board frame. It is so easy once you have them made. And they are flexible for various sizes.

 

Marcia

Share this post


Link to post
Share on other sites

I use a thin sheet of plexiglass. It gives a mirror smooth surface for the bottom and plaster won't stick to plexiglass.

I use the cottle board frame. It is so easy once you have them made. And they are flexible for various sizes.

 

Marcia

 

 

Great idea Marcia I think I'll go with the plexiglass.

 

Evan

Share this post


Link to post
Share on other sites

One thing to consider is that I made my box out of cheap pine that wasn't very straight. The video I watched on making cottle boards (from Ceramic Arts Daily) said to use oak or birch plywood. That stuff has to be pretty expensive comparatively if I even knew where to get it. Home Depot has oak boards but they are very expensive. I don't remember ever seeing oak or birch plywood there. I guess the good thing is that cottle boards are adjustable and once you bear the expense of making them, they can be used many times.

 

Another problem is that I don't have a suitable base to put the cottle boards on. In one video the instructor suggested using something like a formica counter base I believe. What are you folks using?

 

 

No need to use oak or birch, just use plain old pine or any other inexpensive wood. Mine are pine and are nice and straight and have been used for years and only get better with age. Just use any wood that is straight and smooth. You can set them on any work table. I spray a little WD40 on the table first then use the cottle boards. If I want an especially smooth bottom to the mold I set my cottle boards on my grand piano.

 

Jim

 

 

Jim,

 

Do you really pour molds on your grand piano???

 

Evan

Share this post


Link to post
Share on other sites

One thing to consider is that I made my box out of cheap pine that wasn't very straight. The video I watched on making cottle boards (from Ceramic Arts Daily) said to use oak or birch plywood. That stuff has to be pretty expensive comparatively if I even knew where to get it. Home Depot has oak boards but they are very expensive. I don't remember ever seeing oak or birch plywood there. I guess the good thing is that cottle boards are adjustable and once you bear the expense of making them, they can be used many times.

 

Another problem is that I don't have a suitable base to put the cottle boards on. In one video the instructor suggested using something like a formica counter base I believe. What are you folks using?

 

 

No need to use oak or birch, just use plain old pine or any other inexpensive wood. Mine are pine and are nice and straight and have been used for years and only get better with age. Just use any wood that is straight and smooth. You can set them on any work table. I spray a little WD40 on the table first then use the cottle boards. If I want an especially smooth bottom to the mold I set my cottle boards on my grand piano.

 

Jim

 

 

Jim,

 

Do you really pour molds on your grand piano???

 

Evan

 

 

No, just joking because I'm always warning people to never depend on the glaze to prevent leaks and I use a vase someone thinks they've sealed with glaze on a grand piano as an example to the point that I'm sorta known here for that and my hatred of splash pans. The clay should not leak with no glaze on it. Obviously, that needs to be pointed out from time to time since just a few days ago someone who has been potting 40-something years mentioned depending on the glaze to seal his pots. I wish I had a grand piano--so I could sell it.

 

Jim

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

By using this site, you agree to our Terms of Use.