Plastic Casts

[Andy]

I have a question for those of you who have experience making plastic castings of your work. It's not as hard as I expected but I can't seem to eliminate the air bubbles that plague the finer details of the engraving. I realize it's a surface tension thing. I have tried vibrating the mold after filling but there isn't much time because it starts setting pretty quick. Another question....the literature calls for heating the mold. Do any of you do that, and if you do, what is the best way to go about it without melting the mold Any advice is appreciated.

 

[sam]

I never had any luck with getting bubbles out either. Maybe a vacuum system's the answer.

 

[pilkguns]

I only have expereince with Aluma-Lite, and they are very helpful about answering questions and (knock on wood) I seldom have bubbles if done correctly. I heat the mold* and I use fresh material. Most of the time I paint the mold as well. either silver or gold. The shelf life seems to be pretty limited from what I hear from Aluma-lite staff, so I buy it only direct from Aluma-lite. They are also very picking about shipping it to you, if it's too hot or too cold, they will ask you to wait a few days for the temp to moderate. If you get a batch that is starting to bubble on you, then buy a fresh batch. I will do a thin layer with the new stuff and then mix up the old stuff and poor in to fill the mold completley, letting the new stuff dry first of course.

* I have several of those radiator type oil filled heaters. I put a cookie pan on top of them and then my molds on top of the cookie pan, so that the molds are about 150 degrees or so I would guess.

 

[Ron Smith]

Andy, It is dificult to make copies without bubbles, but here is what I do that helps a bit. 1. You can dust a little talcom powder onto the mold before pouring and blow out excess. This acts as a release agent. It only helps. The chemical reaction is what causes the bubbles and it sets up so fast I don't think a vacume would help and be to slow to get the bubbles out before it set up. A slower acting polymer would work with a vacume. Look at your local craft shop for casting polymers that you might try. I haven't made any castings in a good while and polymers came under different nems because they had discontinued some of the types, but you might have to experiment.
2. You can spray the mold with a clear lacquer that will create a barrier between the surface of the casting and the bubbles.
3. Sometimes if the casting media has been sitting on the shelf too long it effects the chemical reaction.
4. There are some other two part polymer products that work better than alumilite. I presume that is what you are using. I have gotten some bad batches of it as I think if it gets too cold, that also effects the chemical reaction and the way it mixes. Also to heat the mold, you can place it under an incandescent lamp a while before you go to casting. Heat slows down the set up period allowing the bubbles to rise from the surface of the mold. I haven't tried this, but you might spray the casting with a clear flat lacquer after casting and maybe it would cover over the bubbles...Maybe.
These are some ideas that might help...............Ron S

 

[Andy]

Thanks for the help guys. Scott, what type of paints do you use? I hate the idea of an extra step but I'm sure it would seal against the bubbles. A silver paint would look more like the original as well. I question how well the paint would hold up. My casts seem to be a tad flexible. Some paints may not handle flexing without cracking.

 

[Mike Bissell]

After making hundreds of castings for the FEGA guild I believe that I have the answer to your question. This doesn’t use the vacuum system, which I understand is one solution. Here is what I do. First I spray paint the mold with a white lacquer. I do this by lightly feathering in the paint from 4 different directions. This to be sure all sides of the detail in the mold are covered. I then let dry for about 15 minutes. Then mix and pour in the resin. You can remove the casting in about 30 min. but I will let it set for an hour or more. After removing from the mold I will let it set for a couple of days before I ink them. This gives the paint additional time to cure. The paint method actually seems to help in de-molding and extents the life of the molds. I also use the resin with a 10 minute working time as I usually do maybe 15 to 30 castings at a time. This process will also work with the 3-minute resin. I have found that water even in the form of humidity is an enemy of these resins and will cause bubbles or foaming in some cases. I have tried many different methods and this one is the easiest one that I have done and has the greatest success rate.
Hope this helps
Mike

 

[rhenrichs]

Mike,
What brand of resin and catalist are you using? Marty seems to have it down pretty good. He had a bunch of casts in Reno that looked pretty good.
Hey Andy, good question. I've had the same problem.

Roger

 

[Mike Bissell]

I get my resin from Micro-Mark they have an on-line store (micromark.com). The name of the resin that I use is CR-600 they also have a CR-300 which has a quicker curing time. It comes in two parts A & B. Similar to Aluma-Lite.

Mike

 

[Andy]

I guess another question would be which molding rubber does the best job? I feel I got great results from the Aluminite brand that GRS sold me. I'm going to run out to the hardware store and get some paint....I'll see how that fairs out. Thanks all....

 

[Degs]

You could try brushing in a thin layer of resin, would allow the bubbles to escape easier and the brushing action may help eliminate them. Then top up the mould when the thin layer has gone off. Don't know if it will work, but might be worth a try.

Degs

 

[Mike Cirelli]

Mike I was wondering if you have ever tried Castoldo mold release spray.

 

[Joe Mason]

Mike, What type of ink do you use?

Thanks

Joe

 

[Andrew Biggs]

Mike Bissell has hit the nail on the head. When I first made some castings it drove me nuts. I was doing it in the middle of winter in the garage and it was a disaster. I use Aluminite and ended up making the castings in the living room. The worst bubbles were the small pin prick ones that weren’t visible till you inked the cast, then it just looked like a black smudge on the casting.

I set up small fan heater to keep all moisture away and let it gently blow over the area I was casting. This had the effect of heating the mould which helped a lot as well. It also kept away moisture from either cold or humidity. When the resin is poured into the mould, flick it with your fingers quite hard a few times and this gets rid of a lot of the bigger bubbles.

Aluminite bring out metallic powders (silver/steel and brass/bronze) that you can dust into the mould before casting. A small jar will last you just about forever. Dusting the mould with white lacquer works really well as it puts a barrier between the resin and the pin prick bubbles, sort of like a skin.

Cheers
Andrew

 

[Mike Bissell]

Andy - The silicon rubber material that I use is a product from Micro-Mark and is called "one-to-one". This is a pour able rubber and works well if you can use that type of application.

Mike C. - I have tried the mold release spray, but sense I started using the lacquer I don't need a release agent.

Joe - the type of ink that I use is Speed Ball Block Printers Ink Black. Most important get the oil base type the water base does not work well in this type of application

 

[Bill Tokyo]

A Completely Ignorant Question--from a beginner

I'm curious why you want to make plastic castings of engravings.

From all the comments, it seems very common, but think ashard as I can, I can't figure out the purpose.

"This small person regrets their slender abilities"

Bill

 

[Andrew Biggs]

Hi Bill

The answer to that is very simple and comes in two parts.

Casts are as close to the real thing as you can get. As a study aid they are invaluable. Photos only show so much. With the casts you get the third dimension and that is depth. You can see the depth of cut, the size of the peice engraved, the width of cut etc. They really give you an excellent perspective of where you want to end up. I have brought several over the last couple of years from FEGA (www.fega.com) and I'm surprised they havn't worn out as they have been under the microscope that much. They were and still are an invaluable part of my learning.

The second reason is that they are really cool to have. I've got castings from Lee Griffiths, Ron Smith, Sam Welch and a whole lot of others. They are all beautiful and are a real pleasure just to look at. Hang them on the wall and they look fantastic as all of them are minature works of art. They also act as a great way to show your work. Sort of like swapping baseball cards or something similar between engravers.

Buy a few and you'll see what I mean.

Cheers
Andrew

 

[Bill Tokyo]

Thanks for the answer!

Hi Andrew,

Thanks very much, this gives me an added perspective on engraving.

Bill

 

[sam]

This is an excellent thread, and I've copied several of the posts to the Tips archive. The exchange of information here is incredible, and I appreciate everyone's contributions! / ~Sam

 

[Sandy]

Andy,
There is a way to mix the two liquids together so the bubbles don’t form. As you know the bubbles form behind the stirring stick when you are mixing. The more vigorous you stir the more bubbles you get. Instead of stirring them, fold them into each other. This is done with a thin artist spatula on a piece special paper. I get the paper from Brownells. The only draw back is your working time. Folding the resin and hardener together takes more time but the bubbles do not form. To fold the parts together you slide the spatula under the liquids and fold it over onto the top of the glob. You can see the mixing as the two parts come together. Do this for about a minute or until you feel they are thoroughly mixed. If you take the time and be cautious there will be no bubbles. It pours off the paper with no problems. Again the only draw back is your working time.

Sandy

 

[FANCYGUN]

Sorry it took me so long to jump in here on the castings. I was back east at my sons graduation.

I dust my molds with Talc and blow them out prior to casting with alumilite. You do have to make certain that the talc is fresh otherwise if there is the slightest bit of moisture..you will get those devastating fine pits that will destroy any inking of the image. I forgot to do that and had to throw out a whole bunch of castings last year before reno. So cast up a few and ink them in before yu go hog wild.