Friday, 15 April 2011

Mould Making - Hands & Feet

Its time to start a Mould Making Marathon.
A lot of the characters in our film require flexible body parts. Our three main characters need silicone components including hands, feet, arms, legs, necks and even hair. That means a lot of rigid two part moulds need to be made, and the process of making them can be very delicate and time consuming.
The duty of moulding and casting all these parts has fallen to me (Josh craftily escaped).

I've spent nearly two weeks moulding and casting all the parts for the puppets. Its an exhausting process but the results are looking good. I'm going to spread the whole moulding and casting process over a few posts, starting with Hands and Feet.
In this post I will be moulding a pair of hands for the Theatre Usher and feet for the Mail Man.

You can see my earlier post about moulding the Mail Mans hands HERE and I'm using the same technique.

Theatre Usher Hands
Above you can see the Theatre Ushers hands that were sculpted by Josh. They were sculpted in Plastiline over the wire hand armature. These hands are chunkier and larger than the Mail Mans due to the Ushers larger size. You can see the characters design HERE.
A wall of terracotta clay is built up around the sculpt, half submerging the hands. The hard part is getting between each finger. It takes a lot of patience. I've used yellow Plasticine blocks to act as 'keys'. These tapered blocks will help the two halves of the mould line up and fit together.

A foam board box was built around the clay and hot glued together (making sure its water tight). I applied Vaseline to the inner edges of the box and sprayed 3 layers of wax release agent over the sculpt. Release agent stops the resin from sticking to the clay. Once that had set, I poured Polyurethane Resin into the box and used a brush to make sure no air bubbles stuck to the sculpture surface. I topped up the resin, filling the box up roughly 1cm above the hands.

 
After the resin had cured I removed the foamboard box and flipped everything over. The terracotta clay was peeled away leaving the sculpted hands half submerged in the resin. Any remaining clay was washed away with water and a soft brush.. Above you can see the hands in the resin. I added more plasticine to the mould surface leaving a 1cm gap around the sculpture. These will lower the contact surface area of the mould, making it easier to separate the two halves. A new foam board box was then built around the mould.

After spraying the surface with 3 more coats of wax release agent, I poured the second polyurethane half. It's very important to use release spray. If I didn't the two resin halves would fuse together trapping the sculpture inside.Once that had set I removed the mould from the box and gently pried the two halves apart. The plastiline sculpture was removed from the resin and the mould was cleaned with Turpentine. Turps melts away clays like plasticine and plastiline. I will explain more about that later when I post about casting.

Mail Man Feet.

As you can see above, Josh has sculpted a nice pair of shoes over the feet armatures I made earlier.
You can read Josh's post about sculpting the feet HERE

Choosing where the split line will be is an important part of mould making. A seam line will be visible on the silicone castings. These are found where the two halves of the mould meet. Its best to try and disguise them so they won't be visible, but its also important that the two halves of the mould are able to be separated. This means there can't be any large undercuts.
The split line for the feet is concealed along the sole of the shoe. As before the clay was surrounded by a foam board box and release agent was added.
Above you can see the mould ready for the second half of the resin to be poured.

The Polyurethane resin is mixed in equal parts. Once it has set it turns an ivory colour. The resin cures quite quickly but the the mould making process is still very lengthily.

These two moulds are the first of many. I will be posting more pictures of the mould making process and they were all made using this general technique. In my next post I will show the finished sculpture of the actresses body parts and the moulding process.


31 comments:

  1. Thanks for sharing this wonderful tutorial on your mold making process! I look forward to seeing your molding technique for the actresses body parts.

    ReplyDelete
  2. Hi there,
    Thanks for the post - I'm trying to create a silicone puppet at the moment and was wondering what type of polyurethane resin you used for and what you used to cast the feet with.
    Thanks, Toby

    ReplyDelete
  3. Toby-
    I believe any Polyurethane 'Fast Cast' resin will work. The brand I used was 'Biresin G26 Urethane Resin' from Tiranti.co.uk
    The feet and other flexable body parts were cast in T20 Silicone from Tiranti.
    I can also highly recomend AnimationToolKit.co.uk
    http://www.animationtoolkit.co.uk/categories/Silicone%7B47%7DMould-Making-/
    Hope this helps.

    ReplyDelete
  4. Thanks a lot Nathan, you're a massive help to me,
    Toby

    ReplyDelete
  5. Oh and one more question, 'did you use any catalyst with any of the silicone casts?
    Thanks, Toby

    ReplyDelete
  6. Toby-
    Yes, catalyst is awlays mixed into the silicone. Thats what causes the chemical reaction that turns it from a liquid into a solid rubber. Without catalyst all you'll have is a runny, gooey mess that will never set.
    If you mean did i use catalyst booster to accelerate the curing time, then yes, I also used that.

    ReplyDelete
  7. Hello,

    First of all, thanks for sharing you're wonderful works !!

    I tried few times to make a resin mold, but i've got all the times bubbles to the mold. You said that you use a brush to avoid air bubbles : is it like for silicon casting, applying a first layer of resin to make sure that no air bubbles will stick to the mold ?

    ReplyDelete
    Replies
    1. Gilles-Alexandre

      Yes that's exactly right.
      I brush on a thin layer of resin using a soft brush.
      Make sure you brush over the whole sculpture to knock away any bubbles from the surface. Once that has set I top up the rest of the mould.

      Im glad you find my blog useful :)

      Delete
  8. Your 2 part of the mold are made ​​of clay and Polyurethane Resin Cast Fast're good here and I'm asking as many questions as I am French and I do not understand English very well

    ReplyDelete
    Replies
    1. Hi Flo.
      Yes the molds are made from Fast cast (Polyurethane Resin).
      Alternately, you could use plaster.

      Delete
  9. soon as possible to make a silicon mold with the skin

    ReplyDelete
    Replies
    1. FLO

      I would not recommend using 'Silicone Skin' to make molds.
      Instead you should use a silicone that is designed for mold making, such as -
      http://www.tiranti.co.uk/subdivision_product_list.asp?Content=T28+Silicone+Rubber+-+Silicone+Rubber+-+Mouldmaking&Subcategory=51&Subdivision=175

      Delete
  10. ok thank you very much for your help
    and I ask many questions because I'm only 15 years

    ReplyDelete
    Replies
    1. Hay no problem.
      I'm happy to help :)

      Delete
  11. hello nathan the two mold parts are the same it is with silicone

    ReplyDelete
  12. hi nathan when I mold to make the corp of my character in 2 parts. 2 sticks them and I can not lift my character remained inside
    What is the plaster to use?
    I hope you understood;)

    ReplyDelete
    Replies
    1. Hi FLO
      The 2 halves of you mold are sticking together?
      you'll need to apply more release agent to the surface of the mold before pouring the second half.
      The release agent will act as a barrier and stop them from sticking. You could use vaseline or buy a release agent spray.

      Delete
    2. This comment has been removed by the author.

      Delete
  13. A ok thank you very much for your help nathant and I use plaster for the corp it's good or not ?

    ReplyDelete
    Replies
    1. Yes, Plaster should work fine for mold making.

      Delete
  14. hi nathan
    when I put my silicone skin into the mold there full of bubbles. how I can do;)

    ReplyDelete
    Replies
    1. This is a tricky one.

      You could try thinning the silicone with a little bit of lighter fluid. That might make it easier for the bubbles to rise and escape.

      Other than that it's just trial and error.
      I might take a few attempts to get a bubble free casting.

      Delete
  15. Helo nathant
    I have a question that I intrigue me .why did you do 2 kind of armature .I hope that you understand :)

    http://nathan-flynn.blogspot.fr/2011/03/character-armatures-continued.html

    ReplyDelete
    Replies
    1. Hi FLO,

      I made the wire armatures when I was at University because they are quick and inexpensive to make.
      After I graduated I decided to upgrade them to ball and socket joints.

      Delete
  16. This comment has been removed by the author.

    ReplyDelete
  17. Ok because i'm making the wire armature like you and i ask if the wire armature is good or no

    ReplyDelete
  18. hi nathan
    how can i to send my photos of my film Une vie de chien

    ReplyDelete
  19. Hey, these posts are great! Is there a reason you use terracotta clay around the puppet parts? Is it sulphur-free so as not to react with the silicone chemistry? I'm in the process of making my first puppet and was wondering what to surround my Chavant sculpt with, and wondered why you chose that clay particularly.
    Nat

    ReplyDelete
    Replies
    1. Hi Nat,
      Thanks, glad you like my blog.

      I use terra cotta clay because it cleans away easily.
      After pouring the first half of the mold the the clay needs to be carefully removed without disturbing the sculpt. Terra cotta clay washes away with a little water and a firm paintbrush.
      Because the sculpt is oil based plastiline, its unaffected.

      Plus terra cotta clay is dirt cheap, which is a bonus for any student model makers.
      I don't think it contains any sulpher. I've certainly never had any issues with it inhibiting the silicone from curing.

      I hope that helps :)
      Nathan.

      Delete
    2. Hey Nathan,

      That's some great info, answered my question perfectly, thanks a lot :)

      Nat

      Delete