[Katherine Swift]

This question was left on our blog by Cat:

i have a 4 in diameter/16 oz glass ornament (using mold release and breaking off glass after curing). I am looking at doing this in two parts to help the air bubbles escape through the small opening at the top of the ornament. My question is how many drops of catalyst do i need if im doing 8oz at a time? I am using the Clear cast Polyester resin

[Katherine Swift]

Cat,

My first thought is that you may want to do it in three or four pours.  Polyester resin really doesnt like thick pours, so its something to consider.

The next thing I need to know is the volume of the mold.  This is very important in determining how many layers, thickness of layers, etc. to determine how much resin and catalyst to use.  To measure a mold, place a plastic bag inside mold, fill with water and pour into a measuring cup.  You might also find it easier to fill the mold with birdseed or dry rice then pour into a measuring cup.

Report back your findings and lets see what we can come up with!

[catrina]

 to give you an idea of what has happened before when ive tried this

something else to note i am using a pearlescent powder pigment but still keeping it translucent: 

These are all full pours;

1: i Used to much catalyst it shrunk this was exactly 16 oz of the clear cast resin.

[URL=http://imageshack.us/photo/my-images/853/imag0976c.jpg/][IMG]http://imageshack.us/a/img853/6317/imag0976c.th.jpg[/IMG][/URL]

2: I tried a different resin for this one because the local hobby lobby didnt have a larger size of the clear cast not realizing at the time why i had issues with the first one.

[URL=http://imageshack.us/photo/my-images/38/imag1045i.jpg/][IMG]http://imageshack.us/a/img38/6315/imag1045i.th.jpg[/IMG][/URL]

i used envirotex i didnt like the color even though i was going to use it because the LED was in there but the peg on one side snapped clean off.

3: This was my final attempt at the time it looks all nice and pretty just after the pour. lit up with the diode

[URL=http://imageshack.us/photo/my-images/267/imag1051.jpg/][IMG]http://imageshack.us/a/img267/5263/imag1051.th.jpg[/IMG][/URL]

after curing 

[URL=http://imageshack.us/photo/my-images/692/imag1056mr.jpg/][IMG]http://imageshack.us/a/img692/3643/imag1056mr.th.jpg[/IMG][/URL]

i had an issue with this one and the second trial bubbling over the side of the top of the ornament… i left the third one in the ornament because the stuff that bubbled over was still kind of gooey, and there were alot of air pockets left inside too. I ended up using this one and coated it with a couple of clear coats but three months later its still sticky.

which is what has led me to remake it by doing the multiple pours

[catrina]

 it is 16 oz when filled with water

[Katherine Swift]

Catrina,

Can I ask why youre using polyester resin for this project?  You would have to do at least 4 pours since it doesn’t like to be poured in thick layers.

For the bubbles, the best way to fix that would be to pressure cast the resin once its poured into the mold.  At that point, theoretically, any should work, provided your stem is large enough (which it looks to be).

If you don’t have a access to a pressure caster, I suggest our Resin Obsession super clear resin.  You can find it in several sizes in our store here:

https://shop.resinobsession.com/collections/resin/resin-obsession

It’s a very thin viscosity, which makes it unsuitable for doming, but great for molds.  Bubbles rise to the surface and pop easily, which makes it a good choice for this mold. 

If you want to continue to use the polyester resin, heres what I would suggest next.  Find out how much filler (use water, rice, etc.) to get a 1 inch depth in the mold.  At one inch of resin (whatever the volume), you should be able to get away with 4 drops of hardener.  When it comes to polyester resin, the thicker the pour, the less the hardener/catalyst in order to control the amount of heat produced.

[catrina]

 i did it in about 7 layers it came out beautiful i never went over 4 drops of catalyst per once, and decreased the amount down to about 2 drops per ounce once i got to the 5th layer. 

i have two remaining questions though

at the fifth layer i left it cure a lil longer than i should have so that when i poured the next layer in it seeped around the sides of the previous layer will i have issue demolding because of this?

also how long does one have to wait to demold?

Thank you for all of your help 

[Katherine Swift]

Cat,

You shouldnt have a demolding issue, but you may have to sand.  The good news is that polyester can be polished with compound and a buffing wheel, so you should be able to make the area completely unnoticeable.

Im guessing you need about 24 to 48 hours to demold.  The surface exposed to air on polyester resin will remain tacky, so thats not a good way to tell.  Do you still have some resin in your mixing cups?  That can tell you if youre cured or not.

Happy to help!

[catrina]

 I demolded it and to remove some of the glass i ran it under water and then i noticed that extra layer started to peel off like an onion skin might have been from the amount of mold release i used. but it only peeled off to a certain point where it got too thick so that seam is going to need to be sanded down. What would you recommend for polishing after sanding? 

[Katherine Swift]

I like to use Fabulustre and a cotton buffing wheel.

[Katherine Swift]

I have never seen those products sold in brick and mortar stores.

[catrina]

 Thank you do you know of any hardware store that would have that or hobby lobby/michaels? sadly i dont have the time to order it online

[Jill]

great tips here, thanks for sharing! 

[Anoushae]

Hi,

I have a fairly large cast ahead of me (266 oz volume) and I would like to use Polyester Resin. I noticed that no. of drops of hardener for a 1/2″ layer is dependent on the volume…in my case at a volume of 33 oz. it would mean about 132 drops, is that true?

Anoushaé

[Katherine Swift]

Yes, but it also depends on the depth of the casting. There should be a technical data sheet with the resin that tells you so many drops of hardener per ounce of resin per depth (inches or cm) of casting.

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