Concept to Completion - Diary of a Sculpt

[RogerA]

Recently, a friend asked me to produce a sculpture of his wife's dog Penny, a pedigree "Pointer".



Penny is such a pretty dog and we agreed that this would be non-exclusive commission whereby the sculpture would be of this particular dog and he would have the first casting but I would have the right to sell this as a part of the range of products on my retail website.

This is brief picture diary of the course of this commission from concept to casting and hand painting the final product. This piece was intended as a resin casting for hand painting from the outset.

It is important to decide early on what the final medium will be as there are a number of differences both in sculpting techniques and in mould making if you intend to produce a hot or cold cast bronze as opposed to hand painted resin.

The first thing to do is to take as many pictures of the subject as possible. If you cannot take them yourself you need to rely on your client but be specific about the angles and shots you need. If I'm taking my own pictures, I like to use a camcorder, as it gives me a good feel for the character of my subject, which if I'm lucky will get built into my work.

Next take as many dimensions as possible but definitely eye centres, length of head, nose to 'stop', head width and so on. In this case I decided that the sculpture would be to a scale of half-life size. I used Photoshop to scale up a few of the most relevant photo's to working size, I can then use the measuring tool in photoshop for detailed dimensioning around eyes and ears etcetera.

OK now to make a practical start. Hopefully I've accurately visualised the job in my head so I have a good idea what I need for the base and armature. I will need a flat surface for the bottom of the sculpture. Then because this will be cast in a vacuum tank, I need to create a reservoir space for the excess resin that will expand in the mould. Thirdly I need the base for the plaster back-up or mother-mould that I will create around my finished work. Finally I will set this on a work base. The resultant armature and base ended up as below



The base for the back-up or mother-mould will need some registration points - I will use upholstery nails for this later on. For now I am anxious to start sculpting.



I use a fairly hard oil based wax/clay which needs to be heated in an oven to make it soft enough to apply

After every job, I recycle it by melting it down, removing any "foreign bodies" and then pouring it into cup-cake moulds so that I end up with a stock of cup cake sized pieces of clay for future use. I've had this clay so long i can't remember where it came from



Now it is starting to take shape but the ears are a bit out of this world.



I like to use marbles or ball bearings for the eyes in the original if the piece is to be hand painted. They make for realistic reproduction but it is very important to get them at the right height, depth and centres otherwise you can end up with a figure that has eyes pointing in different directions, up down or sideways and it is nearly impossible to correct on the finished casting, even with painting.

I decided to make the short stand from neck to base, look like a piece of driftwood, it seemed like a good idea at the time and I couldn't think what else to do. It seems to work on the final piece.

On to moulding. . . . .

Hope to see you in Part II, thanks for looking

Roger

[RogerA]

Welcome to Part II. Where was I? Oh yes, on to moulding.

If this was a bronze, I would need to do a two piece mould so that a hollow wax could be painted into each side for lost wax casting. However as this is for a resin reproduction, the more joints or seams I have, the more of a nuisance and a disfigurement it will be - so I am going for a single skin silicon mould with minimal cut lines. In this case, just one from base to under the chin. I will make the final cut in the mould with a scalpel. Oops! I nearly forgot the registration points for the mother-mould.



As you can see, I've incorporated a seam divider under the chin in order to give me a guide when cutting mould at the end. The rod coming down from the chin will also act as an air release in the mould to avoid air bubbles becoming trapped.

WARNING: If your model is made with a soft clay or is very intricate you need to make a "block mould" before going to the next stage.If you do not you could damage your original beyond reasonable repair.

A block mould would be the same process up to now except at this point you would build a containment around your clay original and simply fill it full of vacuumed silicon rubber. You will get a perfect reproduction of your original but made with a lot of expensive silicon. You will then need to use a hard copy reproduction to go on to the next stage. Of course if you only want one copy for yourself you can stop here.

As I am making a "skin mould", next I need to protect the my original clay sculpture, I use kitchen foil but you could use cling-film just as well. I like foil because there will be some heat generated in forming the mother-mould and I think the foil helps to reduce the effect on the surface.



I am now going to encase my protected original, in a skin of wet clay in order to form the mother-mould. I use wet clay because it is soft and forms over the original without the need to exert any risky pressure which might cause damage or movement.



I roll out the clay (like baking a cake) with depth guides to maintain an even thickness and then lay it over the model until I have fully encased the original



The pipe was intend as the main feed for pouring the silicon but in the event, I used a different feed. However it was not wasted as it formed a reference for the silicon and a riser for any trapped air.

There are many ways to form the boxing for the mother-mould and there are also a few alternative materials to use for the purpose. This is just the way I did it for this figure.

In order to form two halves, I often use, as in this case, plaster board. It is strong and easy to cut with a jig-saw. Firstly mark out your work as accurately as you can and then cut it out.



This is a little bit simplified but now the plaster board needs to be fitted around the encased original and box shuttering put in place to form the plaster.At this stage, you have to hope your armature was strong enough for it not to collapse, I usually support it underneath to help avoid that situation.

Any gaps around your work piece need to be filled bearing in mind that you need to avoid undercuts or any awkward shapes that might make casting difficult. Also because I've used clay and it will stick to the plaster former I give it a liberal coating of release agent made up of petroleum jelly and white spirit. When I get around to taking the plaster back-up's off later I don't want anything to catch and risk damaging the original.

So now I'm ready to lay on the plaster . . . . . .

Hope you can stay with me for Part III

Thanks for looking
Roger

[RogerA]

Part III - Laying on the Plaster.

I want my plaster mother mold to be as strong and lightweight as possible. Also to avoid damage to my original work piece, I want to minimise the heat generated during the plaster curing process. For these reasons I will make a thin laminated mother-mould using fibreglass strips to reinforce my plaster shell. I use a plaster called Crystacal R and you can find more information on it at www.bpbformula.com



My basic method is to pour a little plaster over the work piece and then soak the strips of Fibreglass in a separate bucket and lay them over the top (pic.2) when I think I have enough on, I poke and prod (pic.3) to try and remove any excess air from the inside surface of the cast. As the plaster starts to harden off, I then form it up at the front and back (top and bottom) and smooth it off (pic.4)

Time to do side 2



This is essentially a repeat of side one. I need to make registration keys in the plaster so that the two halves join correctly and I use a countersink drill bit for this (pic.2) I also need to use the release agent again on this side to stop the plaster sticking together.

You then end up your completed mother-mould all the time hoping of course, that your original artwork is intact inside. We should wait 24 hours now for the plaster to harden and cool off - I rarely have the patience for this as I start to get a bit excited now I'm this close to the end

When you are ready prize apart, ever so carefully, the two half of the mould and peel of the layer of clay. This is the part where I hold my breath - it is inevitable that some surface damage will have occurred but if you have been careful, this should be minimal and easily cleaned up



Before discarding the waste clay, I weigh it to give me a rough idea of how much silicon I need to mix for the mould. The inside surfaces of the plaster will need to be cleaned and sealed before the final stage. Also air bubbles need to be filled, I use epoxy putty for this. I would normally spray paint the inside of the plaster cast with grey primer to complete the sealing process and neaten up the mould but I haven't got the time on this occasion. Before moving on, drill the casings wherever it looks like you might have an air trap or want to provide an escape route for air



To avoid the silicon sticking to the plaster surface when it is moulded, I need to use release agent but I believe that the silicon is affected by white spirit so I use a mix of tap water and washing up liquid which works quite well. You must be very careful when placing the plaster back-ups around your original because any little dink or scrape will be forever impressed upon your casting.

I must ensure that my back-up mould is well taped to both sides and to the base. The pressure of silicon going in is more than enough to burst the seams if you don't. OK, all done and ready to pour the silicon rubber



It is essential that the silicon is de-gassed in a vacuum tank so that all air is removed before it is poured into the back-up plaster. Vacuum tanks are expensive items but the cost can be reduced by buying second hand pumps and making the actual tank yourself but that's another subject.

Ok I'm nearly at the end now. The sculpture is "under rubber" as we say in the trade . . . . .

On to Part IV

Hope your still with me we are just coming to the best part

[RogerA]

Part IV - Removing the silicon and making the first casting
(This is the last of 4 parts)

Having allowed 24 hours for cure, I can now prize the two plaster sides apart to reveal the silicon mould.



First job is to clean off the superfluous bits of rubber (being very careful not to cut into the mould) so you end up with a mould as in pic.2. Next having decided where the cut is going to be we just "confirm" it with a good long and sharp blade. When I am happy that I have cut in enough, I just peel off the silicon. A big surprise! my original is almost perfectly intact, they usually get totally destroyed at this stage

I am now ready to cast my first reproduction and I cannot wait to see the outcome. I will make up a mix of 50% polyester casting resin and 50% white marble dust. I will then pour it into the mould and put it in my vacuum tank to extract all the air bubbles from the casting



In 'pic.1' you can see the reservoir area needed to avoid expanding resin overflowing in the tank. In 'pic.2' I have inserted a threaded rod mainly as reinforcement to stop the casting from snapping at the weak points and also for fixing it down onto the intended hardwood base. 'Pic.3' and I'm peeling off the silicon and HERE IT IS - 'pic.4' my first casting as good as I could have hoped it would be.

The only thing left to do is paint it and fix it on a base. . .
. . . and this is the end result that makes all the effort worthwhile



Thanks for sticking with it to the end I hope you have enjoyed this posting and derived some value from it

Many thanks
Roger

[sculpturedolls]

Thanks Roger! Let me be the first to say what a wonderful tutorial that is.

I've went over it and over it and have learned enough to actually do this myself. Your extra details and tidbits really helped a lot. Like weighing the layer of clay to get an idea of how much silicon to use. This is a great tip because silicone is so expensive and to have a lot of extra waste isn't good. But you also don't want to make up too little or the silicone mold would be incomplete.

Excellent painting of the pointer as well. Just love all spots on the one ear while the other ear is all one color. Penny has such cute markings. Her spirit is sure captured in your sculpture.

Thanks for sharing your knowledge with us!

[sculpturedolls]

Hi Roger,

Just wondered if you ever use the brush on type rubber instead of pouring the silicone rubber in the plaster cast?

I've seen other tutorials say that the first layer that you brush on is most important and a person needs to be careful not to get any air bubbles in it. Does your vaccuum tank remove the bubbles completely and thus eliminate the need to do the brush on type rubber?

I'd be worried that it would be difficult for the thickish rubber to go up in to some of the undercuts or deep indentions by just pouring it in.

Thanks for your insight with this question,

[RogerA]

Hi Tamara,

Thank you so much for the 'vote of confidence' I needed that and thank you also for the follow up questions.

Before I got my vacuum tank, I used both latex and silicon in brush-on form. In either case, the first coat is the most important, as you say and as Lady Rando stated in her tutorial.

In the case of latex, I think it is a great way of mold making unless like me you are casting with polyester resin. There is a lot of heat generated during cure and the latex moulds don't last long whereas it is fine if you are casting with stone or plaster or if you just want a one-off 'master'. I also found that occasionally the latex would pull away from recessed detail and cause a bit of malformation but that might have been something I was doing wrong.

For silicon molding without a vac' tank you can use a thixotropic agent to thicken up the rubber and just butter it on. I know a lot artists use this method but you have to be careful about air pockets in the rubber.

The vac' tank takes virtually all air out of the rubber an eliminates surface bubbles on your casting but I'm glad you asked about eliminating air traps in deep indentations because I forgot to mention it in my tutorial. The places where you get air bubbles can be very embarrassing - the least of which is nostrils

I don't know if others have a different solution but what I do is try and spot a problem (like nostrils for example) and then insert a tiny air release with a very thin needle. When you pull the cured silicon off your original, this tiny little 'sprue' of rubber usually gets pulled off without damaging the surface of the cast and your recess, molds as it is supposed to be. If the sprue doesn't get pulled off, it is easy to spot and remove when cleaning up the mold.

Thanks again

Roger

[Glyntarw]

Hello Roger,
Great job on the tutorial. When I picked your name out of the phone book and rang you for some advice on making moulds you offered your help readily and for free!! That was about 5 years ago and it is good to see that you are still happy to unselfishly pass on your knowledge to others. We have worked together over the last 5 years, become good friends and I think I should call you my mentor. Speak to you soon. (The bill for the nice words will be in the mail )
Adrian

[eikenott]

Roger - this is great! Thanks for taking the time and effort to post this. Now the question is the vacuum pump. I wonder if my wife would notice that her vacuum is missing?

Thank you,
YY ?

[RogerA]

Originally Posted by Yumpin_Yimminie

Roger - this is great! Thanks for taking the time and effort to post this. Now the question is the vacuum pump. I wonder if my wife would notice that her vacuum is missing? . . . . .

Thanks for this YY

As long as you remember to empty the bag, your wife won't notice a thing

Thanks again
Roger

[windsongmeditation]

Roger ..your tutorial was great ……and the sculpture is exquisite.

I had the feeling when I read it that I was right there in your studio.

Thanx for sharing your talent and knowledge…….Bob

[Noadi]

Have you tried 2 stage pours at all when casting? Dan Perez mentions on his website using it to prevent air bubbles in tricky areas.

[RogerA]

Thanks for the question and link to Dan Perez' very informative website. When using Polyurethane resin, I've used a 2 stage pour in a similar way to that shown by Dan in the tutorial and for the same reasons.

Most of the time I use Polyester resin which has very different characteristics. In particular it takes about 30 minutes on average to reach a gel stage and then another 30 minutes to harden off. Being much more viscous it also retains a lot more air from the mixing stage. Also I have the advantage of a vacuum tank which pulls just about all of the air out of the silicon rubber before it is poured over the original for moulding and also out of the resin before and during casting. Generally, I wouldn't need to do a 2 stage pour when casting with the vacuum tank (as long as I've been careful not to leave any air traps in the mould).

Just a point of interest, I believe a vacuum tank would have obviated the need for a 2 stage pour in Dan's example but he would have needed to use a 'urethane with a longer curing time to allow an extra couple of minutes for the process.

[Rob Hendriks]

Great tutorial! Making a good model from observation is one thing,but good molding the model is even so important.Thanks for providing the molding technic.
Rob

[Noadi]

You have a good point, it probably would have helped in his case to use one but as you mentioned vacuum tanks aren't cheap. I'm trying to get into casting and I know I can't afford one yet so two stage pours are the way I'm going for now.