Casting hollow clear parts

[Matheus]

So, I'm working at a archaeology lab and my job here is to create replicas of the artifacts so they can be used for teaching purposes. I'm struggling to find a way to cast clear plastic copies of 19th century Bottles cheaply. Does someone now of a way do Slush cast polyester resin? how to get the polyester surface not to be tachie after it cures? Keep in mind that I live in Brazil and poly-urethane is prohibitively expensive.

Thanks!

 

[Exterminator]

Interesting project!

A couple of questions -

1. Are you using a polyester resin that's specifically designed for clear casting? In the past I've made coloured translucent items, and I've "cheated" by using the standard matting resin. It worked, but the surfaces remained tacky for some time (probably a week or two) before they could be handled without leaving fingerprints.

2. What material are you using for the moulds? I guess you are using silicone of some sort. For clear casting resin, you need to be using "platinum cure" silicone (the most expensive, unfortunately!), "tin cure" will not work, and may leave castings sticky or not cured.

 

[Matheus]

Interesting project!

A couple of questions -

1. Are you using a polyester resin that's specifically designed for clear casting? In the past I've made coloured translucent items, and I've "cheated" by using the standard matting resin. It worked, but the surfaces remained tacky for some time (probably a week or two) before they could be handled without leaving fingerprints.

2. What material are you using for the moulds? I guess you are using silicone of some sort. For clear casting resin, you need to be using "platinum cure" silicone (the most expensive, unfortunately!), "tin cure" will not work, and may leave castings sticky or not cured.

I'm using Castin polyester resin and platinum silicone. The problem is that the resin is taking too long to set wich makes it impossible for slush casting and I think the tacky surface could be a result of the pigment havin a little water in it and messin the cure.

 

[Darksyde13]

Hmm, that is a tough one. Since you are trying for such a thin wall I think the tackiness may be more do to with not enough catalyst. Since it is a heat reaction the smaller/thinner the item the more catalyst you need. The larger/thicker the less you need. A bit counter intuitive but there you go.

As for the casting part you might try playing around the different cure times (amount of catalyst) and wait for one side to gel and move to the next kind of like doing multiples layers but on each side with a little overlap. So just put about a 1/4 inch in the bottom, let gel/near gel, then one side, let gel/ etc. Not sure if al the sides will bond properly but might work.

2nd option if you don't mind the inside being a bit discolored is to use a sacrificial plug. Shape a piece of styrophone to size, seal it with pva glue or some other sealant and then just burn it out or douse it in acetone to dissolve it away.


3rd I can think of is if you had a way of spinning the bottle while it is upright you might be able to keep the resin on the sides till it gels then see if you can’t add in a little more to thicken up the bottom.

Haven't tried any of these before but from my dealings with polyester resin they'd be where i would start.

 

[cavx]

So, I'm working at a archaeology lab and my job here is to create replicas of the artifacts so they can be used for teaching purposes. I'm struggling to find a way to cast clear plastic copies of 19th century Bottles cheaply. Does someone now of a way do Slush cast polyester resin? how to get the polyester surface not to be tachie after it cures? Keep in mind that I live in Brazil and poly-urethane is prohibitively expensive.

Thanks!

Out of all the resins I have played with, Polyester Resins are crap unless you are fiberglassing, then you really don't have much of a choice. So my advice is to avoid these where you can. Sure they have their place, but not the choice for me. Not for casting.

If you want an "affordable resin", I'd use expoy (AKA liquid glass) which is water clear and generally cures bubble free, even without degassing (thickness pending). And you can slush it, it just takes longer to kick (35+ min in the Aussie heat.) but works quite well.

Many people I have spoke to about this stuff say to stay away from it due to the heat it produces and how it will burn the silicon molds. Let me tell you, yes it can get hot, but no where near as hot as polyesters. And there is no smell and no tacky feel at the end, so a win win there.

The only issue I have ever had with epoxy is if you add a pigment, it tends to retard the cure time from said 3 hours to almost 6 hours and the parts are soft for a further 12 hours. This actually works in my favor for the parts I make with this, but might be a pain casting a bottle that you want to keep "round" unless you can afford to shelve it for 12+ hours or have a jig made up to keep the "shape" of the part until it fully cures.

The stuff I use is a 1.0:0.5 mix ratio and costs about the same as that nasty polyesters you buy in hardware stores. It just works better.

You'll probably want a high shore silicone (30 to 40) for the molds too, so they self support. A pipe with a larger diameter than the bottle would be ideal for a mold wall. Cylinders also use about 40% less silcone than a square base mold of the same width.

 

[robn1]

I also recommend epoxy, a casting epoxy like the type use to make clear lenses seems best to me as it's made to be completely clear. The table top type will also work, but may take longer to cure.

I haven't had any luck slush casting with epoxy, as it just beaded up on the mold surface. But roto casting a hollow part should work better. I've cast small parts and made thin wall laminations and it never got more than moderately warm, so temp isn't a concern.

 

[PoopaPapaPalps]

What I would do is make a mold like for break-away theater glass, where the bottles are empty but the bottom is missing. You would have to make the mold in three parts: the outer positive and two interior negatives to plug top, inside and bottom. That way you could pour in your epoxy (or polyester if you chose that route) into the mold and then just plug the mold and wait for it to cure. Do a mold for the bottom and then piece the two together afterwards.

That's the route I would go, anyway; I've never had luck slush or rotocasting either epoxy or polyester.

 

[Darksyde13]

I had another thought later this evening. Have you tried sugar or isomalt? Might make for a tasty alternative to all the chemicals!

Isomalt https://www.youtube.com/watch?v=jqPcQT98umU

Sugar https://www.youtube.com/watch?v=GqkSDkHOots
https://www.youtube.com/watch?v=44SGDcOjZH8

 

[cavx]

I had another thought later this evening. Have you tried sugar or isomalt? Might make for a tasty alternative to all the chemicals!

Isomalt https://www.youtube.com/watch?v=jqPcQT98umU

Sugar https://www.youtube.com/watch?v=GqkSDkHOots
https://www.youtube.com/watch?v=44SGDcOjZH8

There is one word that comes to mind when playing with sugar in a tropical climate - ANTS.

 

[udog]

Hi
I´d go for the plug/core way.
Clear epoxy as said above will give you a higher quality casting.
As for the tackiness, it´s part of the exothermal reaction happening, tweaking the cathalyst ratio up could help (also said above) depending on the thicness.
Bear in mind clear polyester wont be as strong as glass, for example, in the same thickness.
You can get rid of the tackiness ( a normal one in a completely kicked casting) by sanding and polishing with the propper polishing paste. We do that in the studio sometimes, tackines is part of the contraction process.
Another interesting product is Crystal Clear (smooth on), less fragile. but a bit tricky (tin silicone molds need postcuring). No sure if its Pu anyway.

 

[Matheus]

Hmm, that is a tough one. Since you are trying for such a thin wall I think the tackiness may be more do to with not enough catalyst. Since it is a heat reaction the smaller/thinner the item the more catalyst you need. The larger/thicker the less you need. A bit counter intuitive but there you go.

As for the casting part you might try playing around the different cure times (amount of catalyst) and wait for one side to gel and move to the next kind of like doing multiples layers but on each side with a little overlap. So just put about a 1/4 inch in the bottom, let gel/near gel, then one side, let gel/ etc. Not sure if al the sides will bond properly but might work.

2nd option if you don't mind the inside being a bit discolored is to use a sacrificial plug. Shape a piece of styrophone to size, seal it with pva glue or some other sealant and then just burn it out or douse it in acetone to dissolve it away.


3rd I can think of is if you had a way of spinning the bottle while it is upright you might be able to keep the resin on the sides till it gels then see if you can’t add in a little more to thicken up the bottom.

Haven't tried any of these before but from my dealings with polyester resin they'd be where i would start.

So I don't know if the foam thing would be easy because the bottles have something called a push-up, it's a dome-shaped recess on the bottom and it is a really important aspect of the morphology of the bottles. Thanks for the ideas.

Out of all the resins I have played with, Polyester Resins are crap unless you are fiberglassing, then you really don't have much of a choice. So my advice is to avoid these where you can. Sure they have their place, but not the choice for me. Not for casting.

If you want an "affordable resin", I'd use expoy (AKA liquid glass) which is water clear and generally cures bubble free, even without degassing (thickness pending). And you can slush it, it just takes longer to kick (35+ min in the Aussie heat.) but works quite well.

Many people I have spoke to about this stuff say to stay away from it due to the heat it produces and how it will burn the silicon molds. Let me tell you, yes it can get hot, but no where near as hot as polyesters. And there is no smell and no tacky feel at the end, so a win win there.

The only issue I have ever had with epoxy is if you add a pigment, it tends to retard the cure time from said 3 hours to almost 6 hours and the parts are soft for a further 12 hours. This actually works in my favor for the parts I make with this, but might be a pain casting a bottle that you want to keep "round" unless you can afford to shelve it for 12+ hours or have a jig made up to keep the "shape" of the part until it fully cures.

The stuff I use is a 1.0:0.5 mix ratio and costs about the same as that nasty polyesters you buy in hardware stores. It just works better.

You'll probably want a high shore silicone (30 to 40) for the molds too, so they self support. A pipe with a larger diameter than the bottle would be ideal for a mold wall. Cylinders also use about 40% less silcone than a square base mold of the same width.

What type of epoxy are you using? 1.0:0.5 is a ratio of what to what? The thing with the pigment is reallya problem for me because the bottles have to be olive green. Any idea if using more catalyst would help? If the resing gels and stop moving on me fast enough that I can slush by hand I have no problem leaving it there in the mold so it really cures. My last question is. Do you mix the catalyst and then wait 35 minutes for it to kick and then you pour and slush it? If not, what's your process? Do you have photos or something? Anyway, thanks for the help.

I also recommend epoxy, a casting epoxy like the type use to make clear lenses seems best to me as it's made to be completely clear. The table top type will also work, but may take longer to cure.

I haven't had any luck slush casting with epoxy, as it just beaded up on the mold surface. But roto casting a hollow part should work better. I've cast small parts and made thin wall laminations and it never got more than moderately warm, so temp isn't a concern.

Thanks.

What I would do is make a mold like for break-away theater glass, where the bottles are empty but the bottom is missing. You would have to make the mold in three parts: the outer positive and two interior negatives to plug top, inside and bottom. That way you could pour in your epoxy (or polyester if you chose that route) into the mold and then just plug the mold and wait for it to cure. Do a mold for the bottom and then piece the two together afterwards.

That's the route I would go, anyway; I've never had luck slush or rotocasting either epoxy or polyester.

The bottom is really important for the type of bottle I'm replicating and the replicas are not only for display, they are ment to me used for educational purposes. Thanks for the help.

I had another thought later this evening. Have you tried sugar or isomalt? Might make for a tasty alternative to all the chemicals!

Isomalt https://www.youtube.com/watch?v=jqPcQT98umU

Sugar https://www.youtube.com/watch?v=GqkSDkHOots
https://www.youtube.com/watch?v=44SGDcOjZH8

They are ment to be touched and kind durable, but thanks for the idea.

There is one word that comes to mind when playing with sugar in a tropical climate - ANTS.

You're totally right

Hi
I´d go for the plug/core way.
Clear epoxy as said above will give you a higher quality casting.
As for the tackiness, it´s part of the exothermal reaction happening, tweaking the cathalyst ratio up could help (also said above) depending on the thicness.
Bear in mind clear polyester wont be as strong as glass, for example, in the same thickness.
You can get rid of the tackiness ( a normal one in a completely kicked casting) by sanding and polishing with the propper polishing paste. We do that in the studio sometimes, tackines is part of the contraction process.
Another interesting product is Crystal Clear (smooth on), less fragile. but a bit tricky (tin silicone molds need postcuring). No sure if its Pu anyway.

Thanks for the ideas.

I think this might help. That is a master for one of the bottle I'm trying to replicate.

 

[cavx]

What type of epoxy are you using? 1.0:0.5 is a ratio of what to what? The thing with the pigment is reallya problem for me because the bottles have to be olive green. Any idea if using more catalyst would help? If the resing gels and stop moving on me fast enough that I can slush by hand I have no problem leaving it there in the mold so it really cures. My last question is. Do you mix the catalyst and then wait 35 minutes for it to kick and then you pour and slush it? If not, what's your process? Do you have photos or something? Anyway, thanks for the help.



Thanks.

View attachment 625724View attachment 625725

I buy all my products locally. In Australia, we have basically 2 suppliers - Barnes for the hobbyist and ERA for industrial. I can buy from both because I have an ABN. Products are similar in price for volume. The advantage of ERA is that you can specify a specif shore hardness of their polyurethanes, where you have to buy the standard shore from Barnes. I really like their Vario silicones as well.

The epoxy product I am using for some of my parts is called Epoxycast. It is a 2 part resin where you mix 1 unit of Part A to 0.5 units of Part B. In fact, the hobby kits are 1.5KG, so you already have the correct amounts. Shore hardness on this stuff is A100 so pretty hard. On its own, it seems to cure in the said 3 hours, but when I add white pigment, I get extended cure times. I have not mixed in translucent tints yet. They may not have any affect.

You can buy a 1:1 product as well, but that stuff costs a fair bit more for the amount you get in the kits. These also need degassing for casting as they are slightly thicker and the bubbles will not rise and pop like they do in epoxycast.

For that bottle, I would go with a 2 part mold where the seam is around the sharp edge of the base. You could add a hole in the neck for a roto cast of the part.

 

[Matheus]

I buy all my products locally. In Australia, we have basically 2 suppliers - Barnes for the hobbyist and ERA for industrial. I can buy from both because I have an ABN. Products are similar in price for volume. The advantage of ERA is that you can specify a specif shore hardness of their polyurethanes, where you have to buy the standard shore from Barnes. I really like their Vario silicones as well.

The epoxy product I am using for some of my parts is called Epoxycast. It is a 2 part resin where you mix 1 unit of Part A to 0.5 units of Part B. In fact, the hobby kits are 1.5KG, so you already have the correct amounts. Shore hardness on this stuff is A100 so pretty hard. On its own, it seems to cure in the said 3 hours, but when I add white pigment, I get extended cure times. I have not mixed in translucent tints yet. They may not have any affect.

You can buy a 1:1 product as well, but that stuff costs a fair bit more for the amount you get in the kits. These also need degassing for casting as they are slightly thicker and the bubbles will not rise and pop like they do in epoxycast.

For that bottle, I would go with a 2 part mold where the seam is around the sharp edge of the base. You could add a hole in the neck for a roto cast of the part.

So you are using standard rigid castin epoxy? The molds were done exactly the way you suggested. How long does epoxy takes to Gel so a can stop rotating it?

 

[cavx]

So you are using standard rigid castin epoxy? The molds were done exactly the way you suggested. How long does epoxy takes to Gel so a can stop rotating it?

Correct. The stuff I use has a potlife of about 35min @ 25 degees C. If warmer, it will go off quicker. So in you case (after a small test batch), you might find you can leave on the bench for the first 20min and pour/rotate for 10 or 15min.

The beauty of this stuff is there is no smell or residue like you have with a polyester resin and it costs about the same.

 

[robstyle]

you can heat up the material but be careful as it can have an adverse reaction when dealing with clear materials. The rum bottles for the POTC movies were rotocast by hand out of a clear material that was heated to speed curing but they were also supposed to be flawed.

 

[Matheus]

Correct. The stuff I use has a potlife of about 35min @ 25 degees C. If warmer, it will go off quicker. So in you case (after a small test batch), you might find you can leave on the bench for the first 20min and pour/rotate for 10 or 15min.

The beauty of this stuff is there is no smell or residue like you have with a polyester resin and it costs about the same.

I'll try to find some similar epoxy resin here in Brazil and then I'll post it here and is properties so you guys can see if it fits (I really don't want to waste money from the lab). Do you have any photos of the cast pieces that you get using thi method?

you can heat up the material but be careful as it can have an adverse reaction when dealing with clear materials. The rum bottles for the POTC movies were rotocast by hand out of a clear material that was heated to speed curing but they were also supposed to be flawed.

Our bottles are suposed to be flawed too. I've tried to heat the resin but for some reason it reacted with the pigment and I got really bad results.

 

[BrundelFly]

Crystal Clear by SMOOTH ON is the best Clear castings resin.

I think spin casting those would be best route.

 

[lmgill]

Unless it has to be identical, and I mean tooling marks and dimensions, have you considered just having a glass blower, make a replica of the bottle? By the time you buy mold material and casting material, you could have a half dozen of them made in glass. Jason Klein at Historic Glassworks ( http://www.historicalglassworks.com/ ) made all the bottles for the last Pirates of the Caribbean and has done work for Pompeii, The Hobbit and Ben Hur. He should be able to replicate these bottles.

 

[Contec]

Unless it has to be identical, and I mean tooling marks and dimensions, have you considered just having a glass blower, make a replica of the bottle? By the time you buy mold material and casting material, you could have a half dozen of them made in glass. Jason Klein at Historic Glassworks ( http://www.historicalglassworks.com/ ) made all the bottles for the last Pirates of the Caribbean and has done work for Pompeii, The Hobbit and Ben Hur. He should be able to replicate these bottles.

This.... If you plan to use the bottle like the real thing then just have some blown from real glass.

 

[cavx]

I'll try to find some similar epoxy resin here in Brazil and then I'll post it here and is properties so you guys can see if it fits (I really don't want to waste money from the lab). Do you have any photos of the cast pieces that you get using thi method?



Our bottles are suposed to be flawed too. I've tried to heat the resin but for some reason it reacted with the pigment and I got really bad results.

I only have images of cast parts I have made with this stuff.

These are made from epoxy which was degassed. Hmmm, bubble free Generally, this stuff will allow bubbles to raise and pop on the surface, but I like to pull the air out before pouring.

Be sure to use resin pigments, not silicone pigments. In silicone, you can pretty much get away with an oil based paint, but resins want specific pigments and tints that are marked "epoxy and polyester resins". I pay on average about $12 per pot of pigment. You only need a small amount and so the small pots last a long time.

In these parts, the white pigment retards the cure time from 3 hours to over 6. On demolding, the part is soft like that icing on cakes and I am able to them place the part in a jig to ensure the shape is correct as the master part that the mold was made from, is a bit thin on the inside. What that means is I could not wear this part on my shoes if it were not re-shaped on the jig. I let them harden up for another 6 - 12 hours.