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What Is The Difference Between Plaster Of Paris And Pottery Plaster?


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I need to make some new damp boxes. I have to order the pottery plaster online since I have no supplier near me. For 150lbs of pottery plaster they want $75 in shipping! The plaster itself only costs $50.

 

So I am wondering for damp box usage would the plaster of Paris I can get at my local hardware store be ok?

 

T

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I used straight up, old fashioned POP that I got from Home Depot, Pugaboo. I've had zero problems with it, even in my very large (by my standards ;) ) damp box. Just be sure to pop the slab out, once it has set of course, and clean off any residual bits that splash up on the sides during pouring into or mixing in the box. Then take a sure-form, or something like it, to clean the rough edges of your slap before placing back in the damp box. I use a simple green scrubby pad for this and it works just fine for my purposes.

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For a damp box it likely won't make any difference since I'm assuming it's the type with just a slab of plaster.  If it's slip casting molds then it likely would.

 

I've always known regular gypsum plaster to be "weaker" than the Pottery #1.  Your mold will degrade faster and won't hold the detail as long.  I also think they have different absorption rates.

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No mold making just damp boxes.

 

I've made a couple small ones before but just used what plaster I had on hand but it's gone now. This time I am making several large ones to hold assembled mugs, boxes, etc to keep at the leather hard stage for decorating. I dislike having an idea to paint or design then have to spend time making the item I wish to work with, it puts a damper on the artistic muse. So thought I would try large plastic bins about 18x24x12 with several inches of plaster in the bottom to store assembled "blanks". I thought being that big it would be better to use pottery plaster BUT at $75 for shipping plus the plaster itself that causes an issue. I will try plaster of paris if the plaster slab breaks when I pop it out to clean up then I will know I have to fork over the major bucks for pottery plaster.

 

T

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You don't really have to pop the cured slab out of the box, Pug. The main reason for doing so is to prevent small bits from flaking off and getting into your work. If you clean up the slab in place, let it dry thoroughly, and there are no small bits around, you should be safe in just leaving it in the box. As dear old dad always said...."Work smarter, not harder" ;)

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  • 4 years later...

I have some unpainted figurines and s fee small statues That I purchased many years ago with the goal of painting them.  The shop where I bought them is now closed and looking at them I can’t tell if they are bisque or if they are some sort of plaster.  Could anyone here tell me how to tell the difference between the two is there a way you can test it in someway?? They are all white and painted and I remember my late husband And a kiln and fired ceramics and I remember a person need to use different paint On bisque so you can fire it again and then glaze it but I don’t know if these are plaster so I don’t know what to do with them or what kind of paint to use.  Could somebody please tell me how I can figure out what these are made of thank you very much I would really appreciate it if someone could help meCould somebody please tell me how I can figure out what these are made of thank you very much I would really appreciate it if someone could help me figure this out thank you again figure this out thank you again

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Hi Mary!

If the figures are clay, still unknown is the type of clay - particularly, the maturation temperature. A good start might be bring your figures to an experienced potter, then go from there?

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If they are plaster you should be able to scrape  some easily off the bottom,  I can tell if something is plaster by smelling it.  The paint on the statues might keep it from having that distinctive  plaster smell.       Denice

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I poured out my clay on some bats that I made from both PoP and Potters plaster and when the clay was dry enough it pulled up some of the plaster.  Does this mean I didn't let the plaster dry enough or my clay dried too much and will this damage my clay?  It happened with both kinds of plaster just worse with the PoP.

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1 hour ago, AprilW said:

Will it affect my clay?  Do I just need to throw it out?

Not worth taking the risk of having lime pops if you're not sure you can get rid of all of it. 

If you ever make plaster molds you can use the contaminated clay for (unfired) slump/hump molds or forms or walls when pouring plaster, just don't fire it. Just bag it up and label it really well. 

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2 hours ago, AprilW said:

I didn't measure because the videos I watched showed how to do it without measuring.  

Always mix to the manufacturers directions.  After you do it a dozen or so times and recognize how it's supposed to look and feel, you can probably do it by eye.  But if this is something you're just getting into, might want to do it by the book until you've got it down.

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  • 2 months later...
On 2/11/2016 at 12:31 PM, perkolator said:

For a damp box it likely won't make any difference since I'm assuming it's the type with just a slab of plaster.  If it's slip casting molds then it likely would.

 

I've always known regular gypsum plaster to be "weaker" than the Pottery #1.  Your mold will degrade faster and won't hold the detail as long.  I also think they have different absorption rates.

Does this mean I can use regular plaster for slip pours casts? it just means they won't last long. If I only want to make 10 objects. Then I can use regular plaster? I'm just asking. Due to covid and living remote I have no other option. Appriciate the knowledge. Cheers

 

On 2/11/2016 at 12:31 PM, perkolator said:

For a damp box it likely won't make any difference since I'm assuming it's the type with just a slab of plaster.  If it's slip casting molds then it likely would.

 

I've always known regular gypsum plaster to be "weaker" than the Pottery #1.  Your mold will degrade faster and won't hold the detail as long.  I also think they have different absorption rates.

 

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16 minutes ago, Karolina said:

Does this mean I can use regular plaster for slip pours casts? it just means they won't last long. If I only want to make 10 objects. Then I can use regular plaster? I'm just asking. Due to covid and living remote I have no other option. Appriciate the knowledge. Cheers

 

 

Yes you can use normal plaster of paris.  It is just weak and doesn't wick moisture as well.

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