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How to make resin copies
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Escrito por Leonardo Torricini   

After about one year of practice with moulds and new materials, I learned some tricks worth to be integrated to the other tutorials about home made clonation of toysoldiers, to avoid as more as possible the problems of the artigianal printing.
It is about the improvement of quality and to avoid imperfections on the pieces obtained, and consequently to reduce the number of scrap copies. I still haven't find a good way to speed the printing to increase the production, perhaps is a bit the opposite because "soon and well" doesn't go well together, especialy in the artigianal jobs.
I tried to made larger moulds to print more pieces in one time, but I realised that is possible only with very simple pieces without complex shapes and details, the toysoldiers copies with undercuts and fine projections came more or less faulty in about the 70% of cases.
Sometimes an arm, a spear or similar protrusions missing, some other times small empty bubbles on the surface of the copies, often precisely in the place of the nose or of the buttons of the jackets, all places difficult to be filled by the resin, or to be kept full inside till the hardening.
Therefore I concentrate on smaller moulds, big enough for one, or three or four pieces maximum at time, that furthermore are ready after about one week only, the same way to reproduce small objects ("piccoli oggetti", see preceding tutorials), instead than two thick blocks inside a container, just two thinner layers of paste silicon for valves of the mould, open on the sides ond top, these methods are descripted in the preceding tutuorials (only in italian but with clear step to step illustrations).
While making these "thin moulds" is good to integrate all the operations for the accurate and complete covering of the master's surface, to be sure that all the small cavities of the model get comlpetely filled, as decribed for the larger moulds.
Sometimes some copies will come still faulty even printing only one piece at time, but is sure that as less pieces are made at time, as less imperfections will come out.
For a quicker and larger production unfortunatly I think the only way is to get a centrifugal machine or pour the resin inside a void pressurised container, otherwise there is the new proper gear to print real soft plastic pieces, recently discussed on this site forum, this machinery begin to be affordable but is still quite expensive for just an hobbistic use.

Some conversions

These problems tend to discourage the effort, and make the home made cloning unprofitable just to reproduce any model that's is commercialy available, is more convenient to buy a new box of toysoldiers instead to spend one hour to print just an half dozen of copies or few more, furthermore there's the time to prepare the moulds, then there's the cost of the materials but that's the lesser thing.
The cases in wich is particulary worth to use this technique are the reproduction of rare old pieces or conversions, in all cases of very particular and valuable miniatures, but the biggest satisfaction and profit is to ease much the modifications, conversions and the realization of new original pieces from the copies made, and the reproduction of them.

To work on directly, and modify, the soft plastic toysoldiers is possible but there are many limits, while the resin copies are, as we will see, much easyer to be modified in many ways. The only aspect partly negative is that the resin pieces aren't flexible as the common soft plastic, if forced to bend they get broken like the hard plastic ones.
These properties allowed me to realise very quickly (with some other conversion techniques) small new original sets recently pubbished on this website, and the realisation of any new pose I may need.

Working directly on soft plastic toysoldiers, would be hard to modify a piece beyond a certain level, there are some particular toysoldiers in very usefull poses, from wich it's easy to get many variations modifying the relative copies, here's an example of how many conversions can be obtained from the resin copy of the same toysoldier, the Italeri gaul in the middle is a resin copy not modified of the original, all around the conversions.

Another example of simple copies (on the left) and different conversions on the same pieces.


Tips and tricks

The anti-adhesive is necessary to separate the two valves of the mould that otherwise would remain stady glued together, and sometimes also for the master that risk to remain atacched to the silicon.

First we need to consider the material of wich the original is made, the common soft plastic toysoldiers usualy doesn't need waxing if they aren't painted and/or glued, as they're already made of an anti-adherent material. The waxing is necessary on painted and glued pieces, hard plastic, lead and many other materials of wich can be made (or covered) the masterpiece.
In the good modelling shops you can find proper anti-adhesive products, I use the Prochima liquid wax for matt finish to obtain surfaces easy to paint, but there's also for gloss finishing.
It sticks well on every material, leaving an extremely thin layer all around the piece and on the silicon, it helps the separation of the two mould valves and the extraction of the model, reducing much the risk of eventual damages both on mould or master.
It may be layed with a brush, you must cover well all the model, to avoid the loss of details, rather than use less wax, is more important to blow quickly all over the piece, to dry it faster and to prevent any exceding remain over the details.
Is possible also to wax a painted toysoldier but the details will come flatten by the paint further than from the waxing, clean up the waxing afterwards without alterate or damage the painting may be hard or impossible, is better to remove well all the paint before.

AS FOR MANY OTHER STAGES I SUGGEST TO MAKE A TEST WITH SCRAP PIECES BEFORE TO WORK ON A VALUABLE PIECE! - A few silicon under a base, or on a sprue, is enough to check if it will come off easy from the piece or if it need waxing. I suggest also to make some incisions on the part to be tested, if it is flat as under the bases, to simulate the rough parts of the miniature that are the ones that sicks more to the silicon.

For make moulds there are many silicons of different kinds for different pourposes.
The bi-component silicons, liquid or paste with hardener, allow to make very quickly the moulds, with the cataliser they harden in a short time.
The liquid one fills completely any cavity or gap and must be dropped in a container that will give the shape to the mould (as descripted in the preceding tutorials), but has some limits: the master usualy must be steady placed in the right position and height inside the mould container, this to avoid it to "sink" in the silicon.
Same thing for the positioning slots or plugs, that differently from the master must be extracted before the waxing and the dropping of the second part of the mould.
With the silicon in paste instead you need just to make some slot cavities and leave the master deeped as placed, unless it's not a too big and heavy piece that sinks also in the thick paste, as in the case of lead horses and similar (other situation where it's worth to make a test first).

Another problem is the filling of the downfaced cavities, that would remain full of air bubbles just with the liquid silicon dropping, it is necessary to apply a few silicon to fill all the gaps, holes and any cavity on the downfacing side, than the piece must be quickly positioned and deeped in the right place before the silicon applyed drops off. It's also necessary to avoid that the silicon applyed on the model licks on the side that will be up facing.

Another way consist in sacrifying the first half of the mould, that will be made very thin, to limit the waste of material and to ease the removal of it in the extra step, once completed the mould and removed this first valve off, leaving the master still included in the other half, then you must repeat the pour of liquid silicon for the removed part, that being faced up this time will allow all the air bubbles to come out from the gaps, and to reach the surface.

Last limit of the liquid silicon is that the internal surfaces of the mould will come flat and any eventual protruding sottosquadra will remain more or less deeply inside the mould, and therefore very difficult or impossible to be extracted, despite the flexibilty of silicon.

To resolve this problem there are the paste silicons, that allow to shape the surfaces, to create protrusions and depressions for leave the sottosquadras on the surface, and the positioning slots and cavities can be simply digged.

The problem with paste silicons is the opposite of the liquid ones, small gaps and cavities must be filled with a carefull spreading, and as not being self-flattening the internal surfaces of the mould must be smoothed manualy.
There are even "adductable" silicons, they may be applied in many layers, this may help doing complex moulds.

The bi-component silicons are professional products and consequently the price is high unless you don't buy big quantities directly from the producers.

Than there's the common white silicon (the one that remains softer and more elastic), it is almost the same than the paste bi-component but much cheaper, not having catalizer it just needs longer times to harden. There are also other kinds of silicons and gums for the mould making but I haven't experience about these and I can't judge.

There are many possible different shapes for the moulds, depending by the model to reproduce and the printing technique, but the most important thing is the cavity of the model, that must be well positioned respect the shape of the internal surfaces of the mould, to ease the filling of resin and to leave the undercuts on the surface, finaly it must reproduce the model details more exactly as possible.
Pointless to say that some particulary complex models are impossible to reproduce with basic bi-valved moulds, in that cases are necessary composed and multi level moulds, but just in case of extremely complicated shapes, that is convenient to reproduce in parts to be assembled afterwards anyway.
It would be long and confused to talk about the shapes of the moulds, I can say that with some practice it's easy to realise what to do and what don't in each situation, giving a look to the flash line of toysoldiers you can get an idea about this aspect.
Not all the moulds come well, and not just for the imperfections. Sometimes is convenient to make up all the mould again, even if it's good in details and strenght, if isn't well done in the internal surfaces, shapes and cavity position, it is more convenient instead than print many sraps copies before to get a good one just casualy, is just a matter to study well at wich level the flash line must be, or how to give the proper shape to the internal surfaces.

I usualy work with Sintafoam of Prochima, the results are excellent, and is quite cheap, considered that to make a 1/72 toysoldier half centiliter is enough, with the kilogram in the two tanks you can make some hundreds of pieces.
As suggested on the tanks it is convenient to draw the right amount of components with two syringes, than empty both in a bigger one to mix well the resin to the hardener for the 20 seconds necessary, I advise against the use of the bigger "mixer" syringe as injector, I made a mess! It is convenient instead to make a small hole at the end of the scale, to release an air hatch high, and simply drop the liquid resin from the syringe.

Finished the pouring is possible to press out all the remaining resin without big risk of splashes. If you leave the remaining resin to harden completely inside the syringe with the piston completely pressed, is possible to take off completely the remains with the piston, after squeezed gently the syringe with a plier, so you can re-use it many times.

As mentioned we'll examine how to make few copies at time avoiding scraps, air bubbles and missing parts as much as possible. After prepared the mould of the toysoldier with the same technique to reproduce small objects, using paste silicon to make just two thin layers, or also in the other way, but always without air escapes and dropping funnels (see preceding tutorials "riprodurre piccoli oggetti" section), you place the two valves open faced up, once prepared the resin mix you drop it in the cavities of the model, over both the valves of the mould while it's still very liquid.
To prevent empty parts you can bend the mould, to enlarge the small gaps that usualy hold in the air bubbles, and so leave the resin to enter and the air to escape, otherwise with a toothpick (or better a rounded broad knife) is possible to move out or squeeze off the air bubbles from the gaps to make them reach the surface.

The best is to do all these things, this also to spend the couple of minutes necessary for the first hardening of the resin, at that point it becomes a bit thicker and can be piled over the cavity of the model on each valve as a bump, this will make escape the air between the valves towards the sides, avoiding it to get trapped in the master's cavity; at this point, quickly otherwise the bumps will flatten back, you close the valves of the mould keeping them pressed.

All these steps need to be made in 4 or 5 minutes maximum, while the resin is still liquid, otherwise if it harden too much probably will come out empty parts, imperfections or a very thick flash, even it is just a bit too thick as jelly probably you will get some imperfections on the flash line.
While still keeping the mould close pressed, it may be usefull also to rotate it in all the directions for the first minute or two, while the resin is still liquid and till it hardens, so eventual air bubbles probably will move deeper inside the toysoldier instead than on the surface.
Sometimes, evident or internal invisible air bubbles may weaken the model, and also cause the breacking of arms, legs and lesser thick parts.

Then there's to wait for the more or less complete hardening. The copies can be extracted from the mould after various times, a minimal is necessary to prevent the piece to get broken just by opening the mould, but it can be carefully pulled out after just about ten minutes when it is still soft as rubber and easy to bend.
During the first half hour it is still a bit soft and can be easyly cutted, and still bended whith the heat of a flame, differently from plastic it doesn't melt and flatten on the surface, keeping instead all the details on the surfaces of the bended part.
This heat-bending properties decrease quickly and constantly with time and after few hours the resin hardens completely and become similar to the hard plastic, parform it still doesn't melt with the flame, at this point is the ideal for final sanding and file cleaning.

Sometimes unavoidably will still come out some scraps anyway, especialy in case of complex figures.
If there are only small empty bubbles on the surface is possible to correct the piece with putty or dropping some resin in the unwanted holes to fill them.
In case of bigger empty parts it is still possible to try a putty or resin reconstruction, possibly after have replaced the scrap in one half of the mould, then close it between the two valves again and wait the hardening, it doesn't work always but sometimes you can save some sraps in this way.

Now there's to eliminate the flash. If the mould is well done and the print well pressed, the flash will be just an extremely thin skin, that most of the times will come off just pulling it off, otherwise it's easy to be cutted away or filed.
A good deep cleaning of the flash and other imperfections takes a bit of cutter, file or sandpaper work, after the first flash removal I apply a light grey primer, the shiny light yellow color of resin (as the plastic colors of most toysoldiers) hides many details or small imperfections, that instead become evident on the matt grey, so it's much easier to clean up and the finish of the reproduction.
Be carefull around swords, spears, rifles and other long and thin details, the flash must be delicately cutted with shissors or with a good sharp blade, working with the cutter you must place the part on a surface to prevent pressure breakings.
Shissors are good when the piece is still soft, the cutter is better to be used when the piece is a bit harder, for file and sandpaper instead is better to wait one hour or more for a better hardening.

Other long and complex matter that is better to live to the appropriate tutorials.
I can say that conversions are much easier. The resin copies are very easy to cut during the first hour and afterwards is still not difficult, they can be pierced without getting brocken whith pins and needles while still soft, when harder can be carved and drilled whithout big problems, it glues stable, it can be well filed and sanded, it can be bended, and finaly every putty, glue, paint etc. sticks on the surfaces much better and steadyer than on soft plastic.
By my point of wiew all these properties make the resin one of the best materials for the modelling.

Also this new tutorial can be improved and updated, is been possible by the experience and the problems partly resolved, but also by your requests of a better explanation, further to allow a more precise and detailed explanation, they have been a great inspiration for resolve the technical problems.
Therefore I renew the invite to contact me for any problem, explanation or request, even on the forum so everybody can consult it, I don't promise miracles but if is possible I'll do my best to share and improve this technique.