Enamel glaze... on Hydrocal? In a kitchen oven?

[13th Floor John]

I'm a newbie at all this and I need some insight. I'm currently making some Sculpey models that I intend to mold in silicone and then cast in Hydrocal plaster. I don't have access to a ceramics kiln, so the kitchen oven is my only option in the next step: glazing.  I know that regular glaze won't work in a kitchen oven, but I have been hearing of some kind of enamel paint that will act as a glaze over plaster and pottery when fired in a kitchen oven at 300º or so. Will this work?  The models, when cast in plaster, are not intended for food or drink so they don't need to be food safe.  The only videos I've found on YouTube are all about clay pottery, not plaster.

[liambesaw]

It doesn't really act as a glaze, it's more of a hardened paint.  It is prone to chipping and looks like paint.  I think in this instance you may want to try some enamel paint on it, see if it's worth the added cost. And at the same time, try normal acrylic paint and see which you prefer.  Enamel paint may absorb too quickly into hydrocal, so it would also be a good idea to seal or polish it somehow.

Maybe get a small bottle of it first before committing a small fortune on a selection of colors.  

The resulting surface will not be functional of course, enamel paints are not durable enough to eat from.

[oldlady]

when you use the word "model", are you saying that you intend to reproduce that item over and over in some material other than plaster?   if not, what is the intent of these things?

[Bill Kielb]

11 hours ago, 13th Floor John said:

f some kind of enamel paint

Pebeo I think. Acts and looks like paint. Donna Dewberry had great success (non food use) teaching one stroke with acrylics. Airbrush, brush and clear over all seems very doable for decorating these.

http://en.pebeo.com/Pebeo/More-of-Pebeo/Pebeo

Definitely not much like glaze or even China paints actually.

 

[Callie Beller Diesel]

The thing that comes to mind for me is that plaster breaks down with heat. At a quick search for the specifics for hydrocal, I found this quote from the online product sheet: 

“The maximum temperature at which USG Hydrocal White Gypsum Cement molds are safe from calcination is 120 °F (49 °C). With substantial free water in the mold, a higher drying temperature can be used without difficulty.”

It’s referring to drying a hydrocal mould properly to make sure it’s got optimal absorbency, but my question is how friable does hydrocal become when heated to more than twice that recommended range?

[neilestrick]

38 minutes ago, Callie Beller Diesel said:

The thing that comes to mind for me is that plaster breaks down with heat.

I was about to post the same thing! Plaster should not be heated. It will weaken it for sure, possibly break it down quite a bit at 300F. Plaster of Paris is made by heating gypsum to about 300F, so no idea what Hydrocal will do when heated that hot, but I don't imagine it would be good.

[13th Floor John]

 

On 11/30/2020 at 7:23 PM, oldlady said:

when you use the word "model", are you saying that you intend to reproduce that item over and over in some material other than plaster?   if not, what is the intent of these things?

I'm making some Incense burners. They're modeled in Sculpey, after which I'd intended to make silicone molds and then cast them either in Hydrocal or cement.  I was thinking of glazing them with some kind of enamel paint, but I see that putting Hydrocal in the oven won't work. I'll be painting everything else in acrylic EXCEPT the area where the ash will fall - THAT area was the potential glazing or enamel paint area. I'd just like to make sure the plaster (if I cast them in plaster) will hold up to any little coals of ashfall, if you see what I mean.

[13th Floor John]

On 12/1/2020 at 7:14 AM, Callie Beller Diesel said:

The thing that comes to mind for me is that plaster breaks down with heat. At a quick search for the specifics for hydrocal, I found this quote from the online product sheet: 

“The maximum temperature at which USG Hydrocal White Gypsum Cement molds are safe from calcination is 120 °F (49 °C). With substantial free water in the mold, a higher drying temperature can be used without difficulty.”

It’s referring to drying a hydrocal mould properly to make sure it’s got optimal absorbency, but my question is how friable does hydrocal become when heated to more than twice that recommended range?

Ok then, no oven for the plaster. Thank you for that, I appreciate the info.

[liambesaw]

Hydrocal or cement won't burn, no problem.  Paint and enamel will burn, problem.

[Babs]

Stain/ colour plaster prior to pour

[Bill Kielb]

A handful of colors of very high temp paint to 2000 degrees maybe for select areas. Flameproof auto paint if you absolutely must.

[nickicherry]

Any cement colorant will work well with Hydrocal. Buddy Rhodes has a line of concrete glazes that work really well and also act as a sealant. BR also has a line of powdered pigments that you can mix into hydrocal. I've used QuikRete's liquid cement colors as a way to tint hydrocal. The BR glazes have some really nice effects layered over tinted plaster/concrete as well. I haven't tried it before, but I imagine that you could paint designs on using the glazes as well. They chemically react to the hydrocal, so they will be much more durable than paints.

If you want to stick with acrylic paint, I think painting the area where the incense ash will fall with acrylic will work fine as long as you seal the entire object. I've painted hydrocal with acrylics and sealed it with polycrylic with good success.