Attaching separite pieces to complex silicone model...

Hi everyone!

I have created a  silicone model (see attached pic) but it is in separite pieces and I was wondering if I could get some advice on the best way to attach them. The model is made from Platsil Gel 25.

I have bought clear RTV silicone  to attach the piece to the main trunk at its point of contact but am unsure how to get a smooth silicone transition that conceals the - at present - very visible seam. I have been told I can paste silicone over it with more appropriately coloured platsil gel 25, thickened with tinthix. Does this sound feasible? Im worried there might be a transparency that leaves the join visible through the silicone. I am also worried that the new layer wont be smooth.

On a seperate note - I also have slight colour differation between the pieces. I am planning on painting the model with silicone pigments - is this correctable during this process or will I have to recast?

Any info on both these questions greatly appreciated

Tim

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Platsil - a platinum cure silicone.  I use Platsil Gel-10 and Gel-00.  (And also Smooth-On's ecoflex 00-30, another platinum silicone.  Their product Skin Tite is good for sticking silicone.)  

"Tinthix" sounds like it is made for tin cure silicones, if so it may not be compatible.  It is a thickening agent I presume.  

****

Just looked it up, it is made by Polytek, for tin cure silicones.  They also make one called Plathix for their platinum silicones.  That is the one you should get.  https://www.polytek.com/products/liquid-mold-rubbers/silicone-mold-...

It is best to get a good base colour flesh tone with pigments mixed in, and use the same pigments in the silicone you will use for patching and sticking together.  Then, you should be able to paint colour variations onto the surface with a bit more silicone and pigments.

Probably some colour correction possible.  Hard to know until you try.  I make a lot of part B with flesh tone in it beforehand, so there is enough for all the parts I want to cast... except when I stuff up and don't make enough.  But even then I have usually painted a skin layer or 3 onto the mould, and a very slight variation in what gets poured inside doesn't show up much.  

Hi Nick,

Thanks for your feedback. The tinthix/plathix confusion explains why the tinthix thickener I used reacted so aggresively. It thickened up straight away and was like pushing shepards pie around the mould. So a lot of the warts and small bumps I detailed into my clay sculpt havent come out so great on the silicone cast.

I originally thought it was because my sculpt was too detailed.

Do you know if  there small bottles of platThix you can buy in UK at a reasonable price as I can only find large bottles for £20 odd...

Sorry Nick,

One last question - you mentioned using PlatThix with Gel 00 and Gel 10 but is platThix compatible with Gel 25?

Hi Tim

Plathix is compatible with Gel 25. You can even mix Gel 00, 10 and 25 together if you wish to get a different consistency. Handy to know, if you have run out of one type during a mix...

I think I would recast one of the pieces, as the colour difference is quite marked. If you don't, you will need to apply quite a bit of colour to one of them, and this may make the texture contrast too much.

I have used ordinary builder's silicone in the past to add a little section to the bottom of a neck, and was surprised how well it worked, although I did not pigment it as it was to be used to take another cast. My trick was to use plenty of baby powder on my fingertips as I was pushing it into shape. As it is quite thick, it keeps its shape well. Next time I will mix pigment into it. This might be of use to you if you want to repair the missing sections of small bumps etc.

Thanks Simon/Nick,

In relation to Nicks comment:

'I make a lot of part B with flesh tone in it beforehand'

If you mix your colour up with Part B of the platsil gel, does that mean that the colour isnt effected by part A?

I have been doing it the other way round and find when I add the part B that the colour alters/gets creamier.

I have seen people recommending both, but mostly to add to part B. The point about adding enough to do the whole job is to get consistency of colour, and so the colour should be affected the same when adding the other part in proportion. Probably the best thing would be to mix the colour into part B, then make up a small sample blob to check the colour is what you want with it all mixed together. I find the pigments get a bit diluted, so the flesh can look a bit translucent when both parts are mixed. It's really a matter of experiment. I like to keep small samples, so I can make future colours the same.

BTW whereabouts are you in the UK? I'm in the SW, so if you are close by we could meet up to do a bit of silicone casting.

Thanks Simon,

I recast the end of the trunk today - spent a long time matching the colour of the existing torso very precisely - but came out lighter .

Now the main torso is two layers of platsil gel 25 - one painted on - the other sloshed and then expanding foam has been used to fill it out. Because the seperate piece has no foam in it and is really too small to put foam in? im wondering if the same colour is even achievable now.

This is becoming pretty expensive!

I live in Liverpool Simon - but I used to live in the south west - Bristol.

p.s: do you ave any recommendations for what to use to thin down platsil gel 25 for painting colour onto the model? Solvent thinner is the popular one as is naptha but I was wondering if there was a cheaper equivelent like lighter fluid for example as naptha is key ingredient  

What I do is mix up some silicone with maximum retarder and then thin it with lighter fluid, then add colour to paint. You don't need to make up a big quantity, in fact  it's best to keep to very small batches in case it starts to set. 


Got it. The foam colour is affecting the surface colour, so your silicone is fairly translucent. So you will have to do some clever surface colouring if they come out a bit different. It is one of those things that's just awkward. But mixing all your colour in one go into part B for both sections is certainly the way to get it as close as possible.


Tim Ryan said:

Thanks Simon,

I recast the end of the trunk today - spent a long time matching the colour of the existing torso very precisely - but came out lighter .

Now the main torso is two layers of platsil gel 25 - one painted on - the other sloshed and then expanding foam has been used to fill it out. Because the seperate piece has no foam in it and is really too small to put foam in? im wondering if the same colour is even achievable now.

This is becoming pretty expensive!

I live in Liverpool Simon - but I used to live in the south west - Bristol.

Hi Simon

Have managed to get the attachment as close as possible to the original colour so i'm going to join the two pieces today and try and bridge the slight gap with colour washes. 

Thanks for your help and advice on this.

Tim

Simon,

Sorry - I have one more question. I am using platsil Gel 25 to paint the sculpture (withthe lighter fluid you recommended & silicone pigments). Do you know if the ratio for silicone to lighter fluid is the same for Gel 25 as it is for Gel 10?

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