Casting from a Plaster Mold

Part 2 on Casting a 3 Part Mold

 

After the mold is cleaned and left to dry for a few days to a week, it is time to make your first cast.

You can purchase straps to hold your mold together, or in this case, inner tube rubber, cut into strips.

mold cleaned up and ready to cast

This mold is held together by inner tube rubber, cut into pieces

 

Filled with clay slip

Pour the liquid slip carefully into the mold up to the top.

 

You should put on a timer for about 15 minutes at first, keeping a look out for the level of the slip. As the water is absorbed into the plaster, the level of slip will go down.

Mold absorbing water

Top up the slip as the moisture is absorbed

 

You will want to experiment on the timing, but for this casting, 30 minutes is about right to cast a piece. However, this could change depending on how many pieces you cast and how damp the mold gets as well as how thick/thin your slip is.

When you feel that the casting is thick enough, pour half of the slip back into the container and then swirl the remainder of the slip around the casting for a few minutes before pouring it out.

Place the mold onto an elevated prop to allow the remainder of the slip to drip out.

The mold will now take an additional time to dry enough to remove the piece from the mold. In this case it is 30 minutes of drying time.

 

Spout cleaned

Clean the spout hole, being careful to not let the trimmed pieces fall into the sculpture.

 

When dry and ready to remove the piece, clean the spout hole. Take the bindings off from the cast and carefully pull the two pieces apart.

 

mold opened up

One side of the cast has been removed, if the piece is dry enough, carefully pull the sculpture out from the second part of the mold.

 

In this sculpture, the third piece can now be removed as well.

As the pour spout is located at the bottom of the sculpture, we now have to close that opening.

Pour a bit of liquid slip onto a flat plaster bat and place the sculpture on top. This will quickly adhere to the sculpture and create a smooth bottom.

Trimming and cleaning up cast

Here you can see the cast sitting on plaster on top of some liquid slip to fill in the spout hole in the bottom. The opening at the top is also being trimmed.

 

Your sculpture will have seams that can now be cleaned up and you can cut out the opening to the vase, again being careful not to allow the piece to fall into the sculpture.

Bisque fired hand vases

ten castings coming out of the bisque kiln.

 

And there you have it, the end result, bisque fired and ready to glaze.

 

Making a 3 Part Mould

Here are some images and basic instructions on how to tackle a 3 part plaster mold for doing slip cast pottery.  I created this way back in 2014 and posted to a guild that I belonged to, but I thought it would be good on my own site!  My own original sculpture and work.

As for the spelling.  Both are correct, sort of.  It is mould in the UK and mold  in the U.S.  We usually default to the British spelling for many words, but I’m not sure in this case.  So I’ve spelled it mould in the title of this article but mold throughout the post.  I lived for 14 years in the UK, so I’m often thoroughly confused as how to spell anything or even what country I am living in.

Thank you to Angelo diPetta for his advice on how to cast this piece.

original sculpture

Here is the original sculpture. This is going to be a vase with an opening in the top for flowers (or other items) to go into. I’ve had a few rude comments about it, but when it’s full of flowers it’s a hand giving you a bouquet. Behave.

 

Blocking off

Here the model is being blocked off in order to protect the areas that won’t be included in the first half of the casting. The hand looks to be holding something, but that is the shape that will end up as the third piece to be cast.

 

measurements for plaster

Here the area is being measured to calculate the amount of plaster that is used.

 

Always measure using cm.  L x W x H for a rectangular volume or Pi x r squared x H for a cylindrical volume – always use centimetres. This is the required plaster mix. Multiply the number by .6 in order to get amount of water required.

Example: 30cm x 20cm x 10cm = 6000 cubic cm or 6 litres of plaster mix, then 6000cc x .6 = 3600cc or 3.6 litres of water. You could also multiply 6 litres by .6 and get 3.6 litres. This works because 1cc = 1ml. Depending on how much the model displaces the plaster you will have little or more plaster remaining.

cottle boards

This is the cottle board all set up. It’s a bit large for this project but it does the trick.

To see an article explaining cottle boards, visit Ceramic Arts Daily. They have a video about how they work and how to make adjustable cottles.  These ones are made of recycled plastic of some sort.  But you can use wood as well with equal results.  Just be sure to seal the sides with mold soap concentrate so your plaster doesn’t stick to the boards and to make them easier to clean afterwards.

register marks

The piece is set up and ready for the plaster. Ensure that there are no gaps in your cottle boards, that you have a pour spout. In this sculpture the pour spout will be from the bottom due to the shape of the sculpture. That is what the styrofoam cup is for.

 

In this particular sculpture, the part that will be cut out for the entrance to the vase is lower than the highest part of the piece (i.e. the inside of the fist of the hand), so it was decided to make the pour spout at the bottom. After the piece is cast, this can be filled in. The part that is coming out of the hand is for the third piece of the mould.

Mix your plaster and pour it carefully into the cottle. Let the plaster set up and then you can remove the boards, turn over the piece ready to do the second part of the mold.

upside down

This is the piece after the first part of the mold is done. Carefully take away the scrap clay that you used to block off the other side.

 

Ready for part 2

Here is the piece cleaned up and ready to cast the second half. You must seal the plaster with a resist so that the second half of the mold doesn’t stick to the first side. Or you will have one piece that never comes apart. Use mold soap concentrate.

 

I’ve used vaseline or Murphy’s oil soap to create a resist between the two pieces, but it is best to get mold soap from a sculpture or ceramic supplier. You paint a few coats on and let it dry and then clean it off so the surface is nice and smooth. You know you’ve done enough when it buffs up shiny and water beads on it when dropped.  Otherwise you will have a lovely solid piece of plaster, but won’t be able to get it apart.

Be careful not to get any into the inside of the cast, as you need the clay to be absorbed in that part.

Pouring 2nd part

You can now carefully pour the plaster for the second half of the mold. You should always pour the plaster carefully away from the piece you are casting, not directly on the piece, as it looks like I’m doing here. Do as I say, not as I do.

 

There is no image of making the final piece of the mold, but keep the two pieces you have already cast together, and remove the block of clay that was blocking off the last section. Clean as you did for the first casting and make a deep score between the two pieces to create another register. Coat the plaster again with the mold soap and when ready, pour your plaster into the last section. Let it set.

Separating the cast

Now you can separate the pieces. In this case plaster covered the first piece again, so some cleaning was needed to see the seam between the two pieces.

 

Clean up the edges of the mold.  Clean the sides as well, as it will often help you see the seam between the parts you have cast.

If you have a rubber mallet, tap the mold all over – this helps loosen the pieces. Then tap the stiff blade of a knife into the seem, and pry – do this all around the seem line. Sometimes the suction of the clay makes the pulling apart a bit harder.  Be careful though, you don’t want to ruin the cast.

3 part mold

Here are the three parts now opened up.

 

What you should do now is round the corners of the mold and clean it up. This way you don’t have jagged edges that can chip off, and it keeps it neater. Put the mold in a warm, dry area for a few days until it is no longer damp and cold. This mold took 4 days of sitting near a register.

Next: casting a piece with our new mold.

Christmas at the Marshland Centre – Nov 16-17

I will be showing my work in Lakefield on the weekend of November 16 & 17th from 10 – 4pm..  This is a lovely show in a scenic location in Lakefield.  It is boutique style, meaning that all of the artisan’s work is spread around the venue, artfully displayed.  This year is the 14th annual Christmas show, featuring the work of local and regional artisans.

Entrance is free, but you can make a donation in aid of the Lakefield Food Bank or the Lakefield Animal Welfare Society (LAWS).

It takes place at:

Marshland Centre
64 Hague Blvd, Lakefield.

Christmas at the Marshland Centre

Artisanity Show – Nov 1 – 3, 2019

I’ll be participating in the Artisanity show and Sale on November 1 – 3 in Peterborough.  This show includes many artisan crafts such as paintings, wood turning, pottery, gourd art, scarves, ornaments, stuffed animals, jewellery, quilts, felted items and much, much more.  Free Admission, it is a fundraising show for the Artisan Centre, Peterborough.

Takes place at:

Knight of Columbus Hall,
317 Hunter Street,
Peterborough

Hunter St. & Rubidge St.

Artisanity Show & Sale

Learning

Fox from Lisa Naples WorkshopI just came back after a week away in Doylestown, PA from a course with Lisa Naples.  She is a ceramic artist that I have long admired and I had a wonderful time.  We were there a week and the seven other participants (along with me) all making our choice of sitting animal sculptures.  We didn’t know what the others were making until we got to the class.  There was a kangaroo, a sea otter, a ram, a chipmunk, a bird and three foxes!  I was one of the foxes.

I learned so much from this course and look forward to making many more animals in the coming months.  I highly recommend not only this course, but just taking a course once in a while.  It doesn’t even have to be in the discipline that you work in.  A couple of years ago I took a linocut course and it was a revelation!

 

Show in Peterborough a big success

The Kawartha Potters Guild had their annual show at the end of November and it was a huge success.  All the potters’ work was beautiful and sales were up by 20%.  Here is an image of my own display for the show.  Next year is the 20th anniversary and we are hoping to have some surprises for our visitors.

m_sullivan

What Value Art?

There was a lot of talk last week of the sculptures by artist Timothy Schmalz when his sculpture “Jesus the Homeless” was blessed by the Pope on November 20th.  Prior to that, he couldn’t get any church to display the sculptures.  But of course, since the artist and his work got recognition by the Pope, someone has decided that the sculpture (a resin version) may be worth something.

It’s sad that an artist’s work only has value once someone says it has.  The art hasn’t changed, just the perception.

For the article, please click here.