Glass bowl for a slump mold?

[JohnnyK]

Hi All...I am looking to use a textured glass light fitter as a slump mold for a bowl. What should I do to get an effective release from the glass?

[Roberta12]

I use cornstarch.  Some use wd40 (I don't like the smell)  and some use spray veg oil.  Some people use a smooth cloth between bowl and clay.  

r.

[Kelly in AK]

Dry cleaning plastic, it’s so thin. It’ll produce some wrinkly texture but probably allow the texture of the mold to transfer well.

I’ve never tried corn starch for this sort of thing but use it regularly to keep clay from sticking to clay (lids, for example). I’m gonna play with that! 

[irenepots]

I like cornstarch too.  I apply it to the slab then invert in on the mold.

[Babs]

I use thick green dishwashing liquid.Smear liberally

[Mark C.]

I use spray veg oil-as cheap as I can find it.If its an slump mold then the clay needs to comne off very soon as to cracking if its a hump it dries away . I make lots of  fish from glass  this way-most are hump and i tremove them as soon as I can.

[Pres]

I have also used bakers spray for forms to separate especially if using heavy texture also in the mold.

 

best,

Pres

[Mark C.]

For mos forms I use laguna/Axner  Pure lube-I bought a gallon about 20 years ago and will last another 20

https://www.axner.com/pure-lube.aspx

if this does not work I switch to veg-oil spray

[JohnnyK]

And the winner is...oil spray, with the most votes...but, I think I will try each of the methods. The biggest problem that I see with the oil or soap is what to do with the trimming scraps-toss or recycle and how to go about putting a foot on the molded piece after? Would it be best in this case to flatten the bottom and go without a foot? Another option would be to throw the bowl and not worry about the texture. Here's a photo of the light fitter that I plan on using...about 15" diameter.

[Min]

If you use the form as a hump mold you can put the foot on straight after making it. Just make sure to get the clay off the mold as soon as it's set up. If you are going to be making a bunch of these I would make a mold from a thickish slab inside or outside the light cover, about 3/8" then bisque fire it really low, like cone 08 and use that for the mold going forward, won't have to use any mold release if you use bisque for the mold. 

I would put a foot on it, that is quite a wide bowl, having a foot will help support the walls and prevent it slumping during glaze firing.

[JohnnyK]

11 minutes ago, Min said:

If you use the form as a hump mold you can put the foot on straight after making it. Just make sure to get the clay off the mold as soon as it's set up. If you are going to be making a bunch of these I would make a mold from a thickish slab inside or outside the light cover, about 3/8" then bisque fire it really low, like cone 08 and use that for the mold going forward, won't have to use any mold release if you use bisque for the mold. 

I would put a foot on it, that is quite a wide bowl, having a foot will help support the walls and prevent it slumping during glaze firing.

Thanks for the input, Madeline...I have an order for just one bowl and the original thought was to use the glass as a slump mold to pick up the texture. The only reason for making additional versions would be to test the various release methods...

[Mark C.]

Is the texture on the inside or outside? hopefully on the inside 

It needs a foot-thow and attach one

[JohnnyK]

1 hour ago, Mark C. said:

Is the texture on the inside or outside? hopefully on the inside 

It needs a foot-thow and attach one

The texture is on the inside of the glass--outside of the clay. With that in mind, how do I remove the oil to install the foot? Scrape the clay where the foot would be installed?

[Mark C.]

Since its an inside form and dries away from form-I would go with pure mold lube from axner-its not oil based and its easy . I use it on a curved plastic tray sushi form and add a round thrown foot. You could also use plastic  wrap in lower part so oil is not ever put on that part of clay. The oil is an issue so do not use it at attcahment spot

[Babs]

When you scratch ad slip to attach the small amout of lube doesn't affect the fot attaching.

Shouldn't be much trim with molded pots to worry re reclaim.sacrifice it if worried.

[JohnnyK]

Thanks for all your suggestions! I was just thinking, too, that I could put a layer of sand topped with a layer of cardboard in the mold to give the form a wider, flat bottom. That would give me an area to install a foot without having to worry about any kind of release material...

[oldlady]

johnny, i have been doing this for years.  i just use some WD-40 inside the bowl and spread it around, all over with a foam brush.  get it in and out of the texture.  once it is inside the mold it will only affect the clay that you press down into it.  no mess.  smell is not awful.  cannot see enough detail about the bottom.  use a circle of cardboard where you want the bottom to be flat.

[Min]

16 hours ago, JohnnyK said:

I could put a layer of sand topped with a layer of cardboard in the mold to give the form a wider, flat bottom.

Many people like a continuous curve inside a bowl going from rim to rim, aesthetic choice.

[Mark C.]

What Min says is very true-I like that curve as well

Not a flat bottom bowl fan myself

[Rae Reich]

Instead of a foot ring, attach 3 separate leaf-like shapes for feet?

[Joy pots]

Use very thin slip let it dry & make your form.

joy