Object of Intrigue – where to begin?

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The totum I put together was to represent the journey between discovering the Coade Stone Statue on St Botolph without Bishopsgate Church Hall.

Although have investigated the process of casting which could be carried out in many ways, this was absolutely not one of them.

The totum itself is many different materials all requiring different methods of mould making and casting.  However, I wanted to carry out an initial test

to get into the mindset of what problems I would need to address with such a structure.

 

IMG_5228 IMG_5230 IMG_5232 IMG_5246 IMG_5249Thought needs to go into the mould itself and how many parts need to make up the mould.  For some parts of the totum

I would need  a single mould, for others they would need to be, 2 part and 3 part.  Consideration needs to be given to the seam lines, and particularly fixing points,

joints and the stresses and loads at those points.

IMG_5260 IMG_5262 IMG_5265 IMG_5266 IMG_5272 IMG_5275 IMG_5278The chiminea/figurative kiln has an aperture which would need to be sealed, because of the feet, the  overall shape would

require a 3 part or possibly 4 part mould.  The material is porous so consideration would need to be given to the mould material.  The block which has pieces set within, without, and a recess would probably require a 2 part mould and sprigs (additional clay features) added separately.  The figurative column with annotation would need to be a 2 part mould because of the undercut elements. The multiple feature piece would need to be broken down into the separate elements individual moulds prepared and then the whole piece fired as one.

The Coade method was to prepare a clay master model, prepare a plaster mould from the master and then casts were made of the plaster moulds using the pressed mould method.

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IMG_3463 It’s not so great when you discover 1kg of clay has already set when you open the bag!

 

I though whilst waiting for materials to arrive I would go through the process of making to think through issues to resolve.  I decided to use salt dough.  In some ways the materials have the same concept.  The main stiffener I chose to be wholemeal bread flour as it is denser and gives texture and colour.   To give elasticity I added some oil,  to give extra hardness I added lemon juice.

The materials within Coade Stone – Ball clay is the stiffener, the grog gives the stone its texture and colour, the  silica eliminates the craze effect and minimizes shrinkage, as does the grog.   The green clay models are then fired for a period of four days at high temperature 1120 degrees C.  In contrast the salt dough models at ‘fired’ (baked) at low temperature for four hours.

IMG_3464 IMG_3465 IMG_3467 IMG_3472 IMG_3476 IMG_3478 IMG_3523 IMG_3524 IMG_3555This is not the way to make the moulds, however, I wanted to go through the process to better understand why.  The lava rock is a

porous master, as such a mold would need to be made in a way that the many holes and fissures do not suck in the material and prevent removal.   The texture of the lava rock

is something which the sculptor would refine on a green model.  The hourglass is relatively simple with a few undercut details.  Locating nobbles are added for the top mould, in this instance they are cocktail sticks! Again not strictly what you would do, but for the purposes of sketch models it works fine.

The Corinthian column remnant has moulded well and all the inticate detail has been captured.  Overall the moulding process made me understand that the moulds are vital to the process and a considerable amount of time is required to design the moulds and thought given to the material to be used for them and the master you are trying to obtain.

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As mentioned previously the moulds are not the correct material for this, and this is just a sketch model make up.  The porosity of the terracotta clay absorbs the moisture from

the salt dough and so in the case of the hourglass the material becomes stuck to the mould.  If this were clay and plaster the chemical process between the two should eliminate

this happening.  As a contrast I also decided to experiment with a non stick mould.  The clay used for the column remnant faired better however the intricate detail was not picked

up so well by the salt dough.   One of the points of intrigue with Coade stone is that the points of failure were almost always to do with the fixings (iron) and so I would like to look

further into how the different elements can join together.

Interestingly the concept of using the ‘pressed mould’ method on pieces this small was not possible, so this is a variant of that method.

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The end result after the bake.  I used foil to reinforce some of the recesses and fixing holes whilst baking, the salt dough tends to expand, not shrink.

I initially put the items on a baking sheet, then on second thought put them onto a rack to aid the heat transferring all around the models, after a short time

the models had fallen over and the rack marks already set into the models.  Consideration will need to be given on keeping the model(s) stable  within the

kiln.

The totum is certainly not straight, not to any standard of quality, and not particularly beautiful.  However, it highlights all the issues previously mentioned,

and how important the preparation and use of the mould is.  The colour and texture has worked well, some of the detail has  been expressed and the fixing

points I tried have worked, although the top two (column remnant and hourglass)  cannot be fixed in place at the same time.  This is due to the expansion of

the dough at the point of abutment, which I had overlooked.

I need to re-consider my object design and what I am trying to impart from its aesthetic.

IMG_3488Hooray, the Coade Stone materials have arrived…Start over!

 

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