File puptcrit/puptcrit.0707, message 180


To: <puptcrit-AT-puptcrit.org>
Date: Thu, 19 Jul 2007 22:30:25 -0400
Subject: Re: [Puptcrit] TECH: speeding Latex with vinegar


I found some more info about why the latex sets when encountering vinegar.

Makes me want to try making a super-fast molding compound by mixing some 
vinegar with the latex, and pressing that instant goo into a simple negative 
mold.
I don't think it would work for large molds, as the seams might be weak. Or 
not.



After painting the latex on the fabric it must be set so it will adhere to 
the fabric. We do this by adding a

weak acid (like the vinegar we used) to the latex material. Vinegar is 
sometimes called acetic acid. When it is

added to the latex, it reacts with the ammonia. The acidic vinegar 
neutralizes or destroys the activity of the

ammonia and in so doing allows the latex to coagulate as rubber. After all 
of the ammonia has been neutralized

you may notice the characteristic ammonia smell is gone. Of course other 
acids (such as citric acid) could be

used to achieve the same neutralizing effect. In a pinch even a carbonated 
soft drink such as Coca-Cola=A8 or

Pepsi-Cola=A8(which contain phosphoric acid) could be used as the setting 
agent.

source: http://www.polymerambassadors.org/paintinglatex.pdf











----- Original Message ----- 
From: "Mathieu René" <creaturiste-AT-primus.ca>
To: <puptcrit-AT-puptcrit.org>
Sent: Thursday, July 19, 2007 9:54 PM
Subject: [Puptcrit] TECH: speeding Latex with vinegar


> HI all.
>
> I've made a quick test, in a small plaster mold, of speeding rubber latex 
> with vinegar.
> The tip I saw on a sculpture forum said to spray a light layer of white 
> vinegar in the mold, then to spray the rubber latex over it. The ammonia 
> in the latex reacts with the vinegar and the latex sets in reccord time.
>
> Since I don't have the proper airbrush for the task, I'll soon be trying 
> with a pressurised spray bottle (mine just broke before I could try).
>
> But for now, I just sprayed the mold with vinegar, and poured a small 
> quantiy of latex in the mold, rotating until all areas were covered.
> Since I had a much thicker layer than if I had sprayed the altex, I also 
> sprayed some vinegar over the latex.
> It does set much faster than air drying, only a few minutes for a normal 
> layer. But it does shrink a bit, and I have my doubts about structural 
> strenght.
>
> The latex is as rubber-like as it should be, but the feel is different, 
> and it has a funny smell.
> I think it would require extra drying one it is pulled out of the mold.
>
> I have not tried adding more layers, as I didn't have the time to wait for 
> the leftover vinegar to dry before adding more latex.
> I am worried that the bond between latex layers would be MUCH less strong 
> than when using the regular method.
>
> Any chemist in the group to explain the possibilities?
>
>
>
>
> Here is the posti found that mentionned the trick:
>
>
>
> ----------------------------------------------------------------
> You may not only spray the latex to make molds but you can also expedite 
> to make it practically instant which may be news to most of latex mold 
> makers.
>
> You must however check if the viscosity is suitable for the nozzle you are 
> using.
>
> In order to expedite the mold making you may want to mist the master with 
> a very very ligt mist of vinager. The minute the amonnia based latex hits 
> it it will instantly turn into to latex rubber. Once the layer is formed 
> mist it with vinager and latex and on and on until you get the thickness 
> you desire. Make sure you do not over spray vinager. If that happens it 
> may turn runny.
>
> Before you use a master you may want to experiment on a piece. Results and 
> speed of the process may amaze you.
>
> source:
> http://www.sculpture.net/community/showthread.php?t=4149
> -------------------------------------------------
>
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