Smooth-On

I'd love to hear the answers too.. The other day I heard someone talking about a pressure cooker and I was wondering if thats at all anything like a pressure pot? Probably not, but one can certainly dream right? heh

 

Do NOT use a pressure cooker !!!

I do not think that a pressure cooker is meant for the 40-60psi required for cast resin?
They usually come with a 15psi safety valve. I have seen the lid of a pressure cooker
put a good sized dent in the ceiling when the safety valve got stuck, and the lid was
blown off. So please do not use a pressure cooker as a pressure pot.

 

I too have many questions about resins, but that aside, I might be able to help with regard to silicone. I have not heard of difficulty with respect to humidity and silicone mold curing. Resins on the other hand do not react well in very humid conditions. Some of the doll producers in Asia apparently delay pouring resins during very humid times. A dehumidifier or air conditioning in your home or studio will probably be sufficient though.

 

My studio is in the basement of the house. I have a lab-grade hygrometer on the wall which measures the relative humidity in the air. I run a dehumidifier, set at 45. The current reading on my hygrometer in the studio is 35% relative humidity, and it is 79degF. When I run the air conditioner in the house, it will also dehumidify the air.

 

Thoughts on Pressure Pots

I think you can do much better than ~$300.00 USD for a 2.5 gallon pressure pot.

This one is a 5 gallon pressure pot for ~$319.00 USD.

http://www.paintsprayersplus.com/product/JET5PTC/JET-5-Gallon-Resin--Mold-Casting-Pressure-Pot-Tank.html?meta=GBASE&metacpg=JET5PTC&utm_source=gbase&

Internal dimensions are 12-1/2" wide x 11" deep w/ lid applied.

5 gallon Teflon lined carbon steel pressure pot with removable wheels, single air gauge w/regulator and two air relief ball valves. Pot is rated with maximum pressure up to 90 psi.

If you buy a small pressure pot now, and later decide to make bigger dolls, you would have to purchase a bigger pot. If you buy a 5 gallon pot now, you can still make your small dolls, but will have the capability to put larger/more molds in later.

Plus, this is a resin casting pressure pot, not a paint pot, so there are no tubes to remove. The bottom is flat, so if you want to top-load the pot, you can do so easily?

I found this pressure pot by entering pressure pot resin cast in Google.
The company is located in New Mexico, USA.

 

Plat cure is more durable but also more finicky with cure inhibition. Tin cure is cheaper and shrinks more but not extremely so. For starting out, try Moldmax first, then move on to the more expensive plat cures when you have had a bit of practise and you feel your sculpt is "worthy" of good silicone, you could also try Mold star which is plat cured. Because mistakes will be made and material wasted, so better to get a feel for it using a cheaper material than spending more money on a tricky material that may last longer etc (tin cures are getting better these days) and find that you could have done a better job, which inevitably you figure out afterwards.

I wrote a bit about my new 20 litre pot here: http://www.twigling.com/pressure-pots.html, I also have a 10lt pot. In that post there is also a link to another discussion on pressure pots and compressors.

Pressure pots that are set up for casting are very expensive, compared to if you buy one that is intended for paint, and modify it, which is easy if you can find the fittings etc, which you should be able to in a hardware store. I got lucky on ebay with my first pot, and also got my new one on ebay for about half price, a little modification was needed on both.

If you are running with an airbrush compressor you may need to buy a separate tank to store compressed air so you can fill the pot fast when you're casting.

I don't use SmoothOn silicones anymore, as they were too expensive from my distributor in Oz, instead I get plat cures from Dalchem. I use both 25 shore and 35/40 shore hardness rubbers, and the ones I like are translucent. I mix by weight and I use a drill with a paint stirrer to mix them right up. My molds are split block, and in some instances two-part.

 

what about using a pressure cooker for things such as casting in clay slip or plaster?

 

I don't know if the pressure will be high enough to get the bubbles out with a pressure cooker. But for porcelain slip that is to be placed in a kiln later, I imagine pressurising the slip while it's thickening in the plaster mold (best practise if the plaster mold was made in a pressurised situation too, then) would be good to get bubbles out which might otherwise affect or damage the slip castings in the kiln.

 

That is great information, twigling !!!
Once a doll maker has experience with RTV rubbers and PU resin, they can
usually find a supplier more local to where they live, and save much money. For
example, this is an RTV rubber supplier for platinum-cure rubber near where I live:
http://www.silicones-inc.com/history.htm
The library life of the platinum-cure RTV rubber I bought from them is incredible.
The RTV molds I made over 20 years ago are just as nice as when I first made them.

 

When I think about a pressure cooker, I think about STEAM creating pressure.
I just don't think that pressurized steam is good for plaster molds or ceramic slip?
I am not sure where you got the idea to use a pressure cooker for mold making?
It seems to me that I have seen a picture of a dental pressure pot that looked a
lot like a pressure cooker? Using a pressure cooker for a pressure pot just does
not seem like a very good idea to me, at all. YMMV.

There are other ways to make bubble-free ceramic slip castings.
Pour the slip from the plastic jug into a gallon glass jar one day before you use it.
Pour it through a strainer.
Stir the slip before you pour it, it probably settled to the bottom in the plastic jug.
Carefully stir and strain to perfect fluidity.

Make sure your slip has the proper specific gravity and viscosity.
You adjust specific gravity by adding water, and viscosity by adding deflocculant.
Slightly mist your plaster molds before pouring them.
You know, just follow standard ceramic slip casting procedure.

I'm sorry if this is off-topic for this thread.
Please forgive me.

 

My experiences with using Smooth-On silicones -- I started out with Oomoo (tin cure), because it's pretty good if you don't have a pressure pot and it's very forgiving if you don't get the mixtures quite right. Also, it cures fast and is decently priced for the amounts I needed. Mold star (platinum cure) is also pretty easy to use, though I had to be more careful with measurements and also environmental factors. Right now I use Mold Max T (tin cure, translucent) with a shore hardness of 27 and that is fantastic for me (but this one has to have at least a pressure pot). For my initial casts, I use Oomoo because I get more silicone for my money (Mold Star is a little more expensive and then Mold Max T is the most expensive I've used) and mistakes don't cost as much, lol.

I got one of the finish systems pressure pots once I'd practiced the moldmaking for a while and it makes a huge difference in the quality of your pieces and your level of effort. I would go with a modified paint pressure pot over a pressure cooker -- mainly because I don't think it can get a high enough psi to eliminate all the bubbles in silicone. It might work for a low viscosity resin, but silicone is thick, even the low viscosity stuff.

In any case, I would say -- no pressure pot? Stick with Oomoo or Mold Star and the 305 resin. Lots of trial and error, but it'll work. Resin casting is expensive any way you look at it, unfortunately.

 

they do make really tiny pressure pots for dentistry, however I'm not sure how well they'd work. Resin doesn't set up well with water present.

I use MoldMax 30 for all my molds. I only recently started using a pressure pot because San Jose is humid and there's nothing I could do to dehumidify the place(the places here aren't built with much insulation). From my trial and error i found that you want to cast with less than 30% humidity. If you have central air and good insulation you'll probably be alright. You can pick up something that measures humidity for around $10-20. I'm willing to bet a farm store would have something that can measure the humidity in the air for about that price. I got mine from amazon.

You also need to store your resin bottles in a plastic bag with some kind of desiccant.

You can minimize the bubbles you get on your surface when you build your molds by doing the molds in layers. I paint on a thin coat of silicone with a disposable brush, then let that set up completely. Then I paint on 1-2 more layers, making sure to get into weird crevices like noses and lips. Then I do the final silicone pour.

I got fed up enough with bubbles and the humidity here that i saved up and bought a pressure pot.

In the end it's actually a $70 paint pressure pot from Harbor Freight. However the people i bought it from converted it for casting and marked it up to $200.

 

Pressure cookers are not quite the same as pressure pots. They work on the same basic idea (increasing pressure inside to do a specific job), but pressure cookers work by turning water into steam and trapping the steam inside, thus increasing pressure (since water in a vapor state has a larger volume than water in a liquid state). You don't pipe air into it like you would with a pressure pot. Also, pressure cookers have a fairly low psi threshold compared to pressure pots, and in order to get the psi you'd need for resin casting a pressure cooker's safety valve would let pressure out first, or you'd blow the lid off and that's never fun. I'd say save your money for a pressure pot so that you can be safe.

 

Is there a difference between a pressure pot and a pressure tank? A link to what I mean. Pressure Tank

 

I belive that's the same thing cloudedmind. It does say 'pressure pot' in the title too. I think 'pressure tank' may just be another term for the pot.

 

The tanks are for pressure spraying paint. They can be converted for casting, but I don't know enough about pipes to tell you what you need.

 

Thanks both of you. The tank does look similar to the other pressure pots I've seen. I shall have to do some more digging on how well one could be converted.

 

I said this somewhere else, but my pressure casting pot is exactly the same paint pot that Harbor Freight sells for $70.

http://gamerabaenre.com/?p=759 this is how someone else converted that same pot. If you can find someone who's mechanically inclined you can probably get it converted. It seems to mostly be taking off the inner hose and adding the gauges.

 

Thanks Sarah. I totally forgot Gamera had a tut on how he did his. I may need to swing by one of his meets and check out his. That or have my dad or brother help me.