A Shrinking World.
Traditional Japanese robes did not have pockets. Instead they wore a small container on their belt called an Inro. The 'inro' cord was tucked under the traditional wide 'obi' cloth belt and a small carved toggle called a netsuke (pronounced 'netski') stopped the cord slipping back through the belt. Netsuke are generally between one and one and a half inches tall and most are exquisitely carved in the form of animals and other figures.
When I first discovered Netsuke I immediately fell in love with them. There are thousands of different subjects and each one has it's own story, which makes them even more interesting. The most expensive one shown above, sold for £140,000 !. A little out of my pocket money range, so I wondered if it was possibly to carve one for myself !. Unfortunately I do not have an ounce of artistic ability in my body so the only way I thought I would be able to do it was by cheating a little. The problem is that they are so small and contain so much detail. In the end I decided that they were far too small for my aging eyesight and the only way I could possibly do it was by making them really big .... and then shrinking them down in size !. This is what this article is all about.
Polyester resin, on average, shrinks in volume by about 5% as it cures. It really depends upon the amount of catalyst used to cure the resin and whether a filler is used.
When a latex 'glove' mould is made it also shrinks in size as it air cures. Again one can expect about a 5% shrinkage, mainly dependant on the ambient temperature. The more slowly the rubber is allowed to cure, the less the shrinkage. The more times the master is dipped ... the greater the shrinkage.
So the plan was to make a master carving and by a continuous process of making a mould and then making a casting from the mould, followed by making a mould from the casting should enable us to end up with a scale model of the original casting. In theory that is Hi!.
Carving a master.
Almost any non-porous material can be used to make the master carving. I chose polyester resin cast into small blocks, as I would also be using it for the castings. Below is a picture of one blank block of resin and a second that has been roughly sawn to shape. To make life easier, I have glued a picture of the netsuke I want to copy ... onto the top of the block. Click on the thumbnail picture to see it full size.
The drawing stuck to the block is about twice the final size. The next stage is to carve, grind, file or sand the block to almost it's finished size. I will then make a mould of it so that if I screw up carving the detail I do not have to keep starting from scratch again. I can simply cast another and carry on from the last successful stage. Using resin I can also correct serious carving mistakes by repairing it with more resin. By this method I hope to end up with something useful, no matter how many attempts it might take to get it. Watch this space .... but don't hold your breath Hi!.
30 October 2005.
Making glove moulds with Latex.
Natural latex is a safe white liquid and is available from most craft shops. To make a mould one simply dips the master into the latex and then allow it to air cure, which takes a few hours depending upon temperature. When the latex is cured, dust off the outside of the mould with any sort of talcum powder, this aids removal of the mould from the master. Then carefully roll the mould off the master. Dust the inside of the mould with talc to stop it sticking to itself and it also helps prevent air bubbles forming in the castings. Below left one can see the carved resin master for the badgers head blank and a glove mould made from it. All the moulds and castings were made this morning, so it is also a quick process. Latex can 'take up' the detail of a thumb print.
I also decided to have a go at making a mould from the owl that Anne sent me and try to make a netsuke of the resulting castings. The beautiful thing about latex is that it is very safe to handle and does no harm to the master. Usually it requires no release agent on a non-porous master. It is also the cheapest and easiest way of making moulds for resin casting. It is also a very elastic material when cured and this enables it to be removed from masters such as the owl, where the pouring neck of the mould is much smaller than the body, that the mould must 'roll' over when the casting is de-moulded. Below left is the simple glove mould for the owl. Below right is the original owl and a resin casting made from the glove mould.
The original owl is on the left. A really observant reader will note that there are differences between the master and the casting. The reason for this is that the original owl had a number of characteristics that made it unsuitable for use as a netsuke. It was too thin to be a netsuke. So I artificially doubled the thickness of the original owl before I made a mould. I also eliminated some of the sharp edges on things such as the feet and wings. A real netsuke has to feel smooth as any rough edges could damage the clothing. All of these modifications were made without any damage to the master. I simply used plasticine to make the alterations. As soon as the first mould is made the plasticine is removed from the master and the owl is as good as new !. I now have quite a bit of work to do on this first casting before I can make the next reducing mould ... ie, I have to re-carve the feathers on the rear of the casting, do some more work on the feet and remove the sharp edges from the wings ... which will prolong mould life.
Now that we have our first casting we can now measure the amount of shrinkage caused by the process.
Master width Casting width % Shrinkage.
23.24 mm 21. 92 mm 5.67 %
Master height Casting height % Shrinkage.
38.93 mm 36.39 mm 6.52 %
The point to notice here is that the shrinkage is not uniform and if we had to reduce in too many stages we would end up with an obviously distorted figure. In the case of the owl this is not a problem since we are already at the final size. For other masters that we carve from pictures of the original ... we can pre-distort the picture to allow for non-uniform shrinkage. In reality, the average person would not notice this distortion.
I used resin for the Owl, badger and Tomotada's horse because the originals were made from Ivory. Elephant Ivory is now illegal and so modern carvers have to use a substitute. Mammoth ivory is commonly used for the upper end of the market. Polyester resin also makes a very good ivory substitute for both carving and casting. The are many other materials that also lend themselves to casting.
The average person probably thinks that plaster is a fairly soft, crumbly material, but there are hundreds of different types of plaster made for all kinds of applications. Some are harder than ceramic and often used to cast chess pieces, ornaments and even machine tool dies. Plaster is cheap and safe to use, Hardening times for typical casting plasters is about 10 - 15 minutes. By using more than one set of moulds one can cast 100's of items per hour. Below is a picture of the same owl cast in plaster.
Polyester resin requires a certain amount of care in use because of the catalyst (MEKP) used to make the resin harden. I would recommend the use of goggles and plastic gloves when mixing the catalyst with the resin. Resin can be easily coloured and even made to look like metals. For example if we mix aluminum powder with clear resin it looks like polished steel. Cast iron, bronze and brass powders are also available. Probably it's main advantage in this application is that white resin is a good substitute for ivory. Aged ivory is more of a cream colour than white and is never clean. So after casting we need to 'age' the casting. This is normally done by brushing dirt or colouring into the detail and then wiping most of it off again, leaving 'dirt' in the carved detail. Like ivory, resin will take a high polish, can be cut, drilled, tapped, sawn and machined.
When you pour the casting material into the mould only half fill it to start with and then give it a squeeze all over to get the material into all of the detail and all of the air out. Air bubbles can be a problem with any casting material and that includes metals and concrete. The standard way of getting the air out of the mix, is to vibrate the full mould. If anyone is interested, just tell me what size casting you want to make and I will be able to tell you how to make a simple yet effective vibration 'table'.
Normal wax polish can completely change the look of a casting, when it comes out of the mould. Some black resin castings come out looking grey, but a quick polish over with black boot polish will really bring the casting back to life.
Use a calibrated syringe when dispensing the catalyst. This makes sure that you use exactly the right amount each time. There are special calibrated catalyst bottles that are well worth considering.
Resin and plaster is easier to keep off the hands in the first place than it is to clean off them later. Wear rubber or plastic gloves and an old apron and don't spill resin on mothers best carpet !.
Use lollypop sticks for mixing. Special rubber bowls are available that resin and plaster cannot stick to. You just flex the bowl and out the residue pops. Dry clean plastic milk bottles can also be cut down to provide cheap mixing vessels.
31 October 2005
Standing on your own four feet.
There is one school of thought that believes a netsuke should be able to stand up on it's own. It you take a look at Tomotada's horse at the very top of the page you will see things would have to be very finely balanced to allow this to happen. It the feet are not exactly under the center of gravity of the netsuke it will simply topple over one way or the other. So this may be a good time to talk about 'Sprues". Generally when we fill a mould we over fill it and so there is always an extra bit on each casting that has to be removed. This bit is called a sprue. We have several options, we can saw it off, grind it off .... or simple sand it off ... but whatever we do we need to end up with perfectly flat feet on our netsuke, so that it does not topple over. If you are casting many copies of an item it is well worth while making up a simple jig that will always make sure that the sprue it cut off exactly right and save you a lot of time. If you have a little spare plaster or resin it is very easy to make up a block that will always hold castings in exactly the same position and allow the sprue's to be cut off precisely, every time. To see how we can do this let us consider the problems in making a mould for the horse netsuke.
Two Part Moulds.
The simple glove mould we used to make the owl and the badgers head was a single part mould. As you saw, for those simple types of figures they work well and are very simple to make. If you take another look at the horse there are two reasons why we cannot make a single part mould to cast them. First ... assuming that we are going to pour it up side down .... the foot area is far too small to expect to be able to pull the neck of the mould over the wide body of the horse
The other problem is the hole between the legs. If you imagine dipping the horse into latex ... there is no way that you could get the cured mould off the horse !. So in this case we are going to have to consider the more complicated two part mould. However it is still a simple process and once you have mastered it .... there is nothing that you cannot replicate !.
Mould makers use a lot of plasticine or 'play dough' as some people call it. It is basically a clay mixed with oil to stop it drying out. The other thing we need is a small box to make the mould in. The box has no top or bottom to it so it looks more like a simple frame.
The frame needs to be at least half an inch bigger than the horse, all around. It's height needs to be about twice the height of what you are going to cast. I have shown nails but screws would be better to hold the frame together. As you can see our horse sits in the middle on a bed of plasticine about a quarter of an inch thick. Sit the horse on the plasticine and then by adding a bit at a time, build up the height of the plasticine to half the thickness of the horse, including in the hole between the legs.
Next we are going to fill the mould up with a special kind of liquid rubber, turn it over, take out the plasticine and fill the other side up with rubber .... but not yet !. What I have just described would give us a mould in two parts ... top and bottom. The problem is that we always want those two parts to fit together accurately every time we use the mould. To do this we put indentations or 'keys' around the edge of the plasticine. About 5 -6 mm deep will be ok for a mould this size. When we pour the first lot of rubber these indentations will make male locating spigots.
Don't forget the one between the legs !. OK next get a little Vaseline or petroleum jelly on a paint brush and gently brush it all over the horse, plasticine and the inside of the frame. This is a 'release agent' that will stop the rubber sticking to anything.
We are now ready to pour the first half of the mould. Pour the rubber into one corner and let it slowly flow over the horse and plasticine. This will stop air getting trapped on the surface of the horse. Next leave the mould for 24 hours to allow the rubber to set.
The next day turn the frame upside down and very carefully remove the plasticine without disturbing the horse and rubber. Then carefully brush Vaseline over the exposed part of the horse and OVER THE RUBBER !. Otherwise the second lot of rubber will stick to the first ! ... and again around the inside of the frame.
You can then pour in the rubber to make the second part of the mould. Pour it in from one corner and allow it to flow over the horse and rubber, driving the air out as it goes. Now leave the mould rubber to set for 24 hours.
The next day you can remove both halves of the mould from the frame. You will notice that the two halves fit perfectly together, since one part was cast from the other. OK we only have one more job to do and that is to cut the pouring hole for the resin.
Pouring holes, sprue's and air.
Any air trapped in the mould will produce holes in the casting. So we always make sure that air has a way to escape, so quite often in addition to the pouring hole we may want to cut a very small channel for the air to escape through as we pour the resin in. It really depends upon how complex the master was and if it had undercuts in the detail. Now you already know that resin shrinks when setting, so we always need to put a little extra in the pouring hole to compensate for this. We are going to turn the mould on it's side and pour the resin in on one end so we now need to cut a little funnel into the rubber that will lead to the feet of the horse (remember I said we were going to cast it up side down ?. The next sketch shows the position of the pouring hole.
You will see that it was possible for air to be trapped in the tail, so I have cut a small air channel in one half of the mould. Some resin will flow into this channel and form a second sprue but it is very easy to remove it from the finished casting. It also helps if you tap the filled mould carefully on the table as this will also dislodge any air in the mould. Better still use a home made vibration table !.
Back to Sprue cutting !
Now just as we made the first half of this mould we could have used plaster to make a block that perfectly fitted the horse. This block would enable us to cut all feet sprue's exactly right. Think about it !.
1 November 2005
A standing Ovation ?
My Tomotada horse stands on it's own 3 1/2 feet !. I have not yet achieved the delicacy of the original .... but it is in there somewhere !. The left hand leg needs thinning down to start with.
I sometimes forget that I am not carving a replica of a real horse .... only what Tomotada's horse looks like. Still a long way to go.
2 November 2005
Everything you see ....
As you have seen I have been having problems taking macro photographs of little things ... so I have at last had to do the unthinkable ... read the instruction manual !.
OK now the picture is good enough to see what a lousy job I have done with the carving Hi!. Well this is the first carving I have ever done in my life, so hopefully I will improve with time. The other thing is that what you see is 2.5 times bigger than the final item !. The horse is actually standing on a coin (I may mention this coin later!). Now when we reduce the figure we will also reduce any errors. I suppose the next problem I need to tackle is the ears !.
Now I have made a mistake !. I told you about two part moulds but we will not be able to use them until AFTER we get the figure shrunk down to final size. The reason is that the rubber used for two part moulds does not shrink enough !. So I have decided to change my plan and use latex. Yes I know I said that we could not use latex because of the hole between the legs. The answer is to get rid of the hole ! . The other problem was we needed a bigger pouring hole, so what I am going to attempt to do is put the pouring hole on the top of the horse !. This is going to make more work because Everytime we cast we have to clean off the sprue, which will be visible on the top of the figure. We only have to do it while we are reducing the size.
All we need now is a small miracle to sort out the hole !. I need to think about that, so lets talk about mould rubbers and making money !.
All that glitters ..... isn't.
Everyone wants to make money and here is some that I made from metal using the process's we have already covered. Despite my bad photography ... the coins below look and feel like the real thing ... except there never was a solid gold sixpence or gold Maria Teresa Dollar .. and yet there they are before you !.
It is a fact that we can make moulds to cast real metal objects as well as resin and plaster, the only difference is in the type of rubber we use to make the mould.
Mould rubbers ....
Generally metals melt at very high temperatures, far too high for use in the home. However manufacturers have introduced metals such as pewter and white metal that melt at temperatures around 250 degrees centigrade, so they can actually be melted on the kitchen stove. Even at this low temperature rubbers such as latex and vinyl would be destroyed so we need to use a rubber that is specially made for this kind of work, such as high temperature silicone rubber. Silicone rubber will stretch but not as much as latex so it is normal to make a two part mould with it as I described yesterday. When the silicone rubber mould is cured it is capable of handling temperature of up to 300 degree's centigrade for long enough for the metal casting to cool and become solid. This is the only type of rubber that can be used with metals.
Pewter looks like silver when it is polished, but can be made to look like solid gold if a very thin film of real gold is 'flash' electro-plated onto it's surface. This layer of gold is so thin (about 5 microns) that it only costs a few pence to plate a coin. Gold flash plating is also the best way of making pewter look like brass !. A casting shop can probably arrange for electro-plating your castings.
Home metal casting kits are available for making things like metal toy soldiers. Obviously one has to be very careful with molten metal to avoid accidents, so I would always recommend that you get a casting company to do it for you. There are a lot of advantages in not doing it yourself !. First the casting company buys a lot of metal at a time and so it costs them a lot less than it would you. Another reason is the cost of silicone mould rubber, about £20 for a kilogram. Casting companies tend to make their own moulds from vulcanized rubber (old car tubes) and so their costs are much lower. For you they could be even lower .... what you need to do is find a white metal casting shop and make friend's with the owner !. The reason is, you could get your moulds made for nothing using spare mould space !.
Casting companies produce castings for all different kind of business. Usually it costs them about £30 - £60 to have a ten inch vulcanized rubber mould made from 'masters'. A ten inch mould could probably make about 16 toy soldier sized objects with one filling. If the order is only for a few things it means a lot of the customers mould is not used. So it is common to take advantage of spare space for other castings .... like maybe yours !.
A casting company normally sells castings by the weight of the metal used in them. Just to give you a rough idea of costs, I used to pay about 15 pence for small castings and up to £2 for large ones.
Castings need to be polished when they come out of the mould. Again to give you an idea ... the cross in the photograph is not polished and it looked like that when it came out of the mould. Tumble polishing is the easiest to do. Pop the castings into a small lapidary tumbling machine and it does itself !.
There are many other types of mould rubber and for casting resins, plaster, chocolate and concrete , you get what you pay for. Yes I did say chocolate !. How do you think they make Easter eggs ?.
Things like Easter eggs, rubber balls and china ornaments are all made by 'slush moulding'. The mould is usually of the two part type. In the case of Easter eggs, the mould is only half filled with the chocolate and then 'swilled' around until it covers all the inside of the mould, the excess is then poured out and the casting left to set. In the case of ceramic ornaments, 'slip' is poured into the mould. Slip is clay watered down to a thick cream consistency. The hollow casting can be taken out of the mould when it is dry to the 'leather stage'. The first thing you notice about clay castings is that they shrink a lot as they dry !. So that is another method of reducing the size of something. The 'green' clay object is then put in a kiln and baked until it becomes a hard ceramic.
If we poured plaster into a plaster mould it would stick to the mould. To stop this happening we coat the inside of the mould with something that the filling cannot stick to. In the case of plaster going into a plaster mould we would brush the inside of the mould with mothers washing up liquid !. Generally latex needs no release agent unless the master is porous. In the case we would normally paint the master with polyurethane varnish to seal it first. For polyurethane moulds we can use Vaseline thinned down with white spirits. Re-melt able vinyl moulds do not normally need a release agent. Generally , the release agent depends upon what two materials we intend to allow to come together.
3 November 2005