Jeff Longtin

Min - Rather than use roof flashing I use thin plastic sheeting. (I was working at a large corporation, years ago, and they were transiting away from thin plastic sheets, to protect desk tops, to a formica desk top, so I collected lots of thin plastic sheets.)
While the plastic sheets are nice, when I mold round forms, (as opposed to a square pouring box) I sometimes forget that they need to be held down, at the bottom of the shape, as well as strapped together, at the top of the shape, to prevent the whole thing lifting up. (and covering my shoes and pants with a thin layer of plaster splatter.)

I was recently asked about a pouring box for mold making. Here are two versions I use in the studio.  The image with the bulbous object is my main pouring box. The pieces are 3/4" plywood cut into 5"x15" boards. I then screwed 1"x1" strips onto the ends which provide a lip for the small "C" clamps. Very quick and easy to assemble a box in any dimension.
The second image shows another box variation that I use often for flat castings. The sides of the box are 2"x2" pieces of pine. (In his case I also used some 1"x2" strips.) The 2x2 pieces are labeled as "turning blanks" and come in a variety of wood types.  (Woodworkers use them to make stairway balusters.) Because they are square and stocky they don't need much bracing other than a little clay at their base. 
The mold on the left I free formed and did not use the box to limit the plaster. (I shaped it by hand.) The mold on the right I filled the box with plaster and then ran a straight edge along the tops of the wood pieces which resulted in a mold that was evenly thick. 
 

Min - Rather than use roof flashing I use thin plastic sheeting. (I was working at a large corporation, years ago, and they were transiting away from thin plastic sheets, to protect desk tops, to a formica desk top, so I collected lots of thin plastic sheets.)
While the plastic sheets are nice, when I mold round forms, (as opposed to a square pouring box) I sometimes forget that they need to be held down, at the bottom of the shape, as well as strapped together, at the top of the shape, to prevent the whole thing lifting up. (and covering my shoes and pants with a thin layer of plaster splatter.)

I was recently asked about a pouring box for mold making. Here are two versions I use in the studio.  The image with the bulbous object is my main pouring box. The pieces are 3/4" plywood cut into 5"x15" boards. I then screwed 1"x1" strips onto the ends which provide a lip for the small "C" clamps. Very quick and easy to assemble a box in any dimension.
The second image shows another box variation that I use often for flat castings. The sides of the box are 2"x2" pieces of pine. (In his case I also used some 1"x2" strips.) The 2x2 pieces are labeled as "turning blanks" and come in a variety of wood types.  (Woodworkers use them to make stairway balusters.) Because they are square and stocky they don't need much bracing other than a little clay at their base. 
The mold on the left I free formed and did not use the box to limit the plaster. (I shaped it by hand.) The mold on the right I filled the box with plaster and then ran a straight edge along the tops of the wood pieces which resulted in a mold that was evenly thick. 
 

I was recently asked about a pouring box for mold making. Here are two versions I use in the studio.  The image with the bulbous object is my main pouring box. The pieces are 3/4" plywood cut into 5"x15" boards. I then screwed 1"x1" strips onto the ends which provide a lip for the small "C" clamps. Very quick and easy to assemble a box in any dimension.
The second image shows another box variation that I use often for flat castings. The sides of the box are 2"x2" pieces of pine. (In his case I also used some 1"x2" strips.) The 2x2 pieces are labeled as "turning blanks" and come in a variety of wood types.  (Woodworkers use them to make stairway balusters.) Because they are square and stocky they don't need much bracing other than a little clay at their base. 
The mold on the left I free formed and did not use the box to limit the plaster. (I shaped it by hand.) The mold on the right I filled the box with plaster and then ran a straight edge along the tops of the wood pieces which resulted in a mold that was evenly thick. 
 

Looks like Lemon Grove is in southern CA, near the Mexico border.  (If you google it you can actually see the storefront.)
It appears to be located near a place called Plaster City. (A site producing plaster for USG.)
Imagine setting up a mold making studio in Plaster City?

I have mixed up the "Magic Water" recipe and it works. One gallon water, 9.5 gm sod silicate, 3 gm soda ash. 
Soda ash is quite caustic so make sure to wear gloves, or a glove, if you have a cut on your hand. It does sting otherwise.
If I recall the "clay" content was 2/3 clay powder and 1/3 toilet paper.

I have mixed up the "Magic Water" recipe and it works. One gallon water, 9.5 gm sod silicate, 3 gm soda ash. 
Soda ash is quite caustic so make sure to wear gloves, or a glove, if you have a cut on your hand. It does sting otherwise.
If I recall the "clay" content was 2/3 clay powder and 1/3 toilet paper.

If you look in the Community Marketplace someone posted looking for a used slab roller. (In Boulder no less.) 

Years ago I found a book about Belleek porcelain. (I had never heard of the company before finding the book. Apparently, it's an old Irish pottery.)
In the book they showed beautiful porcelain figurines. To allow for variety each appendage, arms and legs, were made with a ball end. The ball end fit into a socket on the main torso form. That way the arms and legs could be arranged in different ways. A huge pain to mold but I did this for the Akita mold. Each leg had a ball like end that fit into sockets on the main torso. As the piece was small there wasn't much room, to move each appendage, but it did allow the artist to play with it as he saw fit. 
 
 

Years ago I found a book about Belleek porcelain. (I had never heard of the company before finding the book. Apparently, it's an old Irish pottery.)
In the book they showed beautiful porcelain figurines. To allow for variety each appendage, arms and legs, were made with a ball end. The ball end fit into a socket on the main torso form. That way the arms and legs could be arranged in different ways. A huge pain to mold but I did this for the Akita mold. Each leg had a ball like end that fit into sockets on the main torso. As the piece was small there wasn't much room, to move each appendage, but it did allow the artist to play with it as he saw fit. 
 
 

I find it best to thin the underglaze to a heavy cream consistency. (or slightly thinner)
When I open most underglaze jars they have a pudding like consistency. Even though the mixture is incredibly smooth I find it goes on incredibly thick. (Hence brush marks.)
As well, I apply coats 5-10 minutes apart. (That way the surface is still slightly damp.) If I wait until the previous coat is completely dry I find it hard to prevent brush marks.
 

Years ago I found a book about Belleek porcelain. (I had never heard of the company before finding the book. Apparently, it's an old Irish pottery.)
In the book they showed beautiful porcelain figurines. To allow for variety each appendage, arms and legs, were made with a ball end. The ball end fit into a socket on the main torso form. That way the arms and legs could be arranged in different ways. A huge pain to mold but I did this for the Akita mold. Each leg had a ball like end that fit into sockets on the main torso. As the piece was small there wasn't much room, to move each appendage, but it did allow the artist to play with it as he saw fit. 
 
 

Yes!  I've gone off and on to Breyerfest since the mid 90's and that is indeed the event I am attending this year in July.  So I want to have a few of these in both sizes and both main versions produced in time to take with me.  I'm also flying out to California to judge a show of equine art and of course want to take some there too.   I also do a number of fine art shows once in a long while but shipping can be VERY costly and I have moved away from paying gallery and show commissions on my sales.  I get plenty of people willing to fight over the pieces I post to public auctions online.
Thank you both for your kind words.  I would love to see your dog pieces, Denise!  I used to sculpt a few dogs as well so if I ever have time I plan to get back to doing that once in a while in between equine pieces.
You are right Jeff that molding a piece like Porthos /can/ be crazy - if I was determined to cast him entirely in one piece, whole.  The issue of his sharply turned head and neck, and the close proximity of his back cocked leg that actually crosses over partly in front of his other back leg, would be ... very challenging to say the least.   So I cut up my 'master' I was molding and I actually cast Porthos in a few pieces.  With practice, assembly and clean up of such a sculpture goes pretty quickly.  I can demold the pieces into a wet box, allow them to firm up a bit, then do the old score and slip-stick routine.  Since I'm the sculptor it is no trouble whatsoever for me then to clean up and redetail those areas I had to attach.  That way it's actually not that difficult to mold such a sculpture as long as you don't mind some assembly.  I can easily put a piece like this together and do all the initial clean up and resculpting in about an hour or less.  Then back into the wet box for slow drying to prevent cracking as he has some uneven thickness in some areas.
To facilitate easier molding I can also flood some minor undercuts such as the tail bow, and simply go back and hand detail those pieces again after casting and assembly.  It does mean I spend a lot of time with post casting but on the other hand I get thousands of dollars per piece once completed so it's well worth my time to make them the highest possible quality I can. 

Beautiful work Hyn Patty. Can't imagine molding it.
Years ago a gent sculpted an Akita dog with as much detail. About the same size as your project. Nightmare project but he was happy with the molds when it was completed.  (He was a breeder and brought several dogs when he picked up the molds. Super strong animals but very well behaved.)
Have you ever heard of Breyerfest? For several years I worked at a pottery shop that made promo mugs for the event. Had no idea what it was until I looked it up. 
Here in Minneapolis the big collectible was little porcelain buildings made by Dept56. Had no idea there was another type of collectible out there.
 

Hey Paula,
How big is your plaster board and how old is it? 
You can "repair" plaster but I find it only works best with new plaster. Presumably your plaster surface has absorbed a lot of minerals, from wedging lots of clay, and that makes it less friendly to new plaster. If you want to try it simply mix plaster, into a milk like thickness, and pour it into the plaster holes. As soon as it loses its wet sheen use a sharp scraper to level off the surface. Do this procedure a few times until you have a smooth surface. It may not absorb as well as the rest of the slab but at least the holes will be filled.
Also, is it not possible to flip the plaster board and use the other side as a new surface?
 

Hey Samantha,
Welcome to the Forum. The kiln looks great. The outside jacket looks fairly clean and the interior bricks look to be in good shape.  The kiln floor looks to be in good shape.
$450 is probably a good price these days.
It uses a kiln sitter to control the kiln so that's just one aspect that you will need to consider. (You have to manually turn up the kiln throughout the firing process.) I've been firing a kiln, very similar, and have had no problems for 25 years.
 

Hello Karen,
Can you post pictures? From my experience only plaster molds can be used with slip casting. I do know folks who have used rubber molds for pressing wet clay but that has its own challenges.
I would recommend you make plaster molds, from your silicone molds, and then use the plaster molds to slip cast. 

Hey Samantha,
Welcome to the Forum. The kiln looks great. The outside jacket looks fairly clean and the interior bricks look to be in good shape.  The kiln floor looks to be in good shape.
$450 is probably a good price these days.
It uses a kiln sitter to control the kiln so that's just one aspect that you will need to consider. (You have to manually turn up the kiln throughout the firing process.) I've been firing a kiln, very similar, and have had no problems for 25 years.
 

Hello Ugly Mug, welcome to the Forum.
The video Peter posted does a good job of showing the process. Creating a bed is the best "first step" in the process. Like the video I choose to make a bed using foamcore. (Its cheap and flat and clean.) I use clay to seal the gap between the shape and the foamcore.
Every so often I coat my plywood pouring boxes with Johnson Paste wax. It won't prevent the plaster from sticking but it makes it easier to separate the plaster from the wood if it does. (If the plaster does stick to the wood just tap it with a hammer to dislodge it.)
I don't tap the bucket or the box. I gently create a wave in the plaster mix and let the bubbles rise that way. 
I like to hold a jiffy mixer in my hand and mix plaster that way. Using just my hand doesn't seem to agitate it enough.  

It's not so much that it will fall off AFTER the firing as much as it will probably fall off DURING the firing.  At which point it will land on your piece in a most undesirable way. Then you have a real annoyance to deal with.
If it's a prized piece run a few tests before you commit to any "attachment" method. (Most fail in my experience.)
As Oldlady suggests it's probably best to sand down the point of the crack, before glaze firing, and accept that it was not meant to be part of the design. More than likely, you'll receive compliments, either way.

Yes and no.  It all depends upon how the model was treated.
As Peter suggests "waste molds" are really only intended to be one time objects. However, sometimes they are so labor intensive that you just want to use it to make a test piece. (To see if it works.) 
Did you have to use lots of mold sealer to make the waste mold? (in other words, is the waste mold really "dirty" from the making process?) 
There have been many times that I have used a waste mold to make a test casting. However, I accepted the fact that it might not turn out, as expected, and it was "just a test".
ps. if the mold parts are "dirty" washing them will help and waiting for them to dry is a good lesson in self-discipline.

Hulk gives good advice, however, there is nothing that says you have to fire on a kiln shelf. You run the risk of the glaze running onto the kiln floor, but if that's a problem you can live with, firing on the floor is no problem. Does your glaze run?
A kiln shelf helps to distribute weight if your piece is heavy. (If your piece is heavy it might stress the bricks if fired without a shelf.)
You might also check to see how much your kiln lid sags.  (If at all?) This too affects how tall you can fire.
Its been my experience that most clays shrink about 5% from wet to bone dry. (At least my cone 6 slip cast porcelain does.) Doing a little test will help you determine the amount of shrinkage of your clay.
As Hulk suggests leaving 1/4" space between the top of the piece and the kiln lid is good. I might make it 1/2" if I'm unsure?

It's not so much that it will fall off AFTER the firing as much as it will probably fall off DURING the firing.  At which point it will land on your piece in a most undesirable way. Then you have a real annoyance to deal with.
If it's a prized piece run a few tests before you commit to any "attachment" method. (Most fail in my experience.)
As Oldlady suggests it's probably best to sand down the point of the crack, before glaze firing, and accept that it was not meant to be part of the design. More than likely, you'll receive compliments, either way.

To give nuance to Peter's suggestions:
The big key is to stretch the clay in lots of directions while you're rolling it out. Will you be making the slab on a slab roller or doing it free hand? If doing it free hand you will want to use various thicknesses of wood sticks to guide you in reducing the thickness. Plop down sticks that are 1" thick and roll the slab. Then pick up the slab, turn it over, spin it 45 degrees. Then roll it with the 3/4" sticks. Pick it up, turn it over, and spin it 45 degrees again. Then plop down the 1/2" sticks, roll the slab again.
Rotating and flipping is the best way to minimize warpage on big slabs. If the clay is too wet you can sometimes stretch it too much at the corners, when you pick it up, so its best to let the clay stiffen a bit between rolls.
Firing the slab is another challenge: are the kiln shelves flat? Is it worth it to go out and buy new shelves that are perfectly flat for the project? (Sometimes it is.) All the silica in the world won't help if the kiln shelf is warped. (Yes, a bed of silica can mitigate a warped shelf but a not warped shelf is the better place to start.)
Clay intended for throwing is considered "plastic". That usually involves shrinkage. Hand building clays tend not to have so much plastic clays in them. Meaning...less shrinkage. Making a large slab is usually best with a hand building clay.
The drywall trick does work well. In place of it several sheets of newspaper, under weight of a flat piece of wood, also reduce warpage in drying.