Maximum Thickness/buildup For Slip Casting

[edwardjones]

Hi, I am new to slip casting, firing slip cast, etc and hope I can get help here with a few beginner questions.

 

I am making a model of a giraffe and want to know what the best method to approach slip casting this form. The body of the giraffe will be hollow after pouring out the un-absorbed slip from the plaster mould but I am worried about the neck and head. The neck will be about 1.5" x 1" x 7" and the head about 1.5" x 1" x 2.5".

 

Should I try to cast this part of the body solid or hollow as the body?

 

Is there a safe guideline or ideal thickness for the walls if not making these parts solid?

 

Is this controllable besides by how much (dwell?) time the slip is left in the mould?

 

Are there tips that anyone can share to casting this shape or firing tips if making it solid? I have read about firing thicker pieces but I understand that this really should be avoided for the known reasons.

 

Thanks for any ideas, help, recommendations, etc!

 

Edward Jones

[perkolator]

at 1" thick, i think you'll be ok casting those parts attached to the body.  any thinner than this is when you start getting into viscosity issues where the legs absorb too much water and "gunk" up, making them solid or semi-solid with a little air pocket in the center.

 

another option would be to make those appendages separate components and cast them separate, then join together when leather hard.  It's really hard to give advice on casting the whole form because there are too many factors like slip viscosity, plaster thickness, plaster dryness, etc that will play in how it actually works out.  my best suggestion is to make it solid, cast it in plaster, then take a positive and cut it up and make another set of molds from that in parts.

[edwardjones]

Thanks for your help. I will give it a shot as is and see what happens. 

 

To make sure I understand, I could make neck and head separate castings from the body. Neck and head could be solid and body hollow. Then once cast join them together?

 

Is there any reference (sites, articles) for joining cast pieces together that someone can recommend? i.e. if at an extreme angle (neck leaning out & not as vertical) will I need armature or supports?

I guess it would be similar to joining other noncasted leather-hard shapes.

 

Thanks again!

[Mart]

Hi, I am new to slip casting, firing slip cast, etc and hope I can get help here with a few beginner questions.

 

.....

 

For start, this mold will be a tricky one to build if this giraffe is anything close to a life like

 

What is the outside diameter for the neck where it gets attached to the head?

The maximum thickness for the walls can not close up narrow areas (like head/neck) and leave you with a hollow head piece with no way for air to escape when firing.

 

Can you start with something simpler? Something, where yo can get away with 2 or 3  pieces.

[edwardjones]

Hi Mart,

The thickness is 1.5"x1", rectangular shaped (not true to life shape) where the head meets the neck.  

Yes, I can and will try something more simplistic to start.

I was worried about the same issue you mention (pockets) and I just wondered if there was a way to leave the slip in longer to allow the head and neck (if needed) to become solid. 

Thanks for your help!

[BeckyH]

One way to help make sure the places that need to be solid are solid is to rest the mold with that part down after pouring put the excess slip. Where is the pour gate going to be on the piece? If the head is at the bottom of the mold, tapping the mold firmly when pouring to dislodge air bubbles, then making sure there is enough slip to fill it when you dump should have the head become solid.

Does that make sense?

[edwardjones]

I was going to use the large body part and could invert for casting if needed. 

 

When firing the slip with a solid neck and head I guess it's better to do slow firings to avoid cracks, etc.

 

So I think my choices are to cut in to multi pieces and make neck and head solid with hollow body or attempt to cast neck and head as solid by putting the smaller objects on the bottom.

 

Thanks everyone!