When to Pull the Vacuum for PR work...

[CameronPotter]

Hi,

Having read what i could find, it said when mixing two colours, you wait until the PR has gelled, then mix the two coloured resins. But if you wait until then, and THEN mix and THEN pull the vacuum, will the bubbles come out?

I doubt it. Hmmmm.

Maybe you need to do it before it gels, (I think I saw this somewhere), but then how do you mix two colours?

Cheers

Cam

 

[terrymiller]

Cameron what type mold are you using. I have tried a flat mold and the ice cube trays. Both ways I did not wait for the PR to gel I poured the colors at the same time carefully not letting the PR colors mix then swirled slowly and carefully. This would probably work for the pressure casting. Or you could pour the first color put it under pressure for a certian amount of time release the pressure pour the second color then re-pressurize them both. I have not tried the pressure method yet but this is the only way that I can think of.

 

[CameronPotter]

Thanks Terry, I will try it without letting it gel.

I am using a block mold (large enough for 6 pens) that fits neatly into a jar for the vacuum.

I think that I will try to mix two colours then stir them very gently and hope that I can avoid disrupting the pattern when shifting it around.

Cam

 

[Skye]

Um, I know I'm new to this, but for this shouldent you be talking 'pressure' and not 'vacuum'? If your stabilizing something, you vacuum. If your clearing bubbles from resin, you pressurize it. Also, you wont want to pressurize a jar.

Maybe I'm just not following though.

 

[CameronPotter]

The best way to do PR is a debatable thing. There are two arguments:

1. Use vacuum, it pulls the air out of the liquid leaving no bubbles at all.

2. Use pressure, it crushes the bubbles the the size where they are no longer noticeable.

I prefer the idea of argument 1. Mind you, there are plenty of good reports using both methods.

Cam

 

[CameronPotter]

Tried this tonight - no luck, the colours mixed while they were left alone.

Damn!

Maybe if I used more hardener, it might not get the chance to do so.

Still, I used red and gold Pearlex, so it looks nice anyway.

Cam

 

[Skye]

I want to say that by looking at the tutorial here, you mix one color in to start, wait for it to jell a little, then pour on the second color. Mix in with a few swipes. But, I've never done it myself.

 

[CameronPotter]

Yeah, but when I do that, I get air bubbles and so I am trying to avoid that problem by using a vacuum. The problem is that the vacuum can't pull air bubbles out of gelled plastic.

Maybe it is a matter of how much to let it gel. [?]

Cam

 

[JimGo]

Cam,
Are you normally getting a lot of air bubbles when you do your castings? I have done several castings using both flat molds and the ice cube trays. In the past, I've never used pressure or a vacuum, and for the colored, solid castings I've never had a problem with air bubbles. I don't use a lot of catalyst, so the bubbles have time to escape the mixture. When I stir the coloring agents into the resin, I try not to introduce too many bubbles, and when I pour, I try to pour the resin along the side of the container this way I don't introduce more bubbles (kind of like pouring beer or soda, though the bubbles form for different reasons).

The only time I've had problems with bubbles is where I'm actually trying to cast something into the resin, especially something that has texture like snake skin. There, if I recall correctly, the air bubbles tended to get trapped close to the surface of the medium I'm casting, rather than being free-standing in the resin itself. That's been my motivation to try the pressure pots and/or vacuum.

To address your other original question, when you mix the colors depends on the effect you want. If you want something like Ed Davidson's blanks, then you want to mix them while both materials are relatively liquid. If you want something that is more crisply deliniated, then you want to wait 'till the first color has at least gelled, if not solidified, before you add the next color.

Here are two of my homebrew blanks that show the difference in the effects:

http://www.penturners.org/forum/topic.asp?ARCHIVE=true&TOPIC_ID=8925&SearchTerms=polaris

http://www.penturners.org/forum/topic.asp?TOPIC_ID=8371&SearchTerms=resin,polaris

 

[CameronPotter]

Thanks Jim.

I am actually getting quite a few of bubbles (or at least more than I am happy with - which would be none).

I am mixing it in a flat mold and cutting blanks after that. I might try your pour down the side idea, but the bubbles from the pour come out pretty quickly, it is the bubbles form the later mixing that are giving me grief (or so I am guessing).

Cam

 

[JimGo]

Cam,
Can you describe your technique in more detail?

 

[CameronPotter]

Okeedoke...

I have tried it a few ways, but here are the basics:

1. Figure out how much resin is needed (I am using clear casting resin).

2. Fill two plastic cups with the resin to the level desired

3. Add any colour I might want to use and any Pearlex I might want to use and stir thoroughly.

4. Add about 1ml of hardener to every 100ml of resin.

Now here is where it get different...

5a. Pour one cup gently into a flat plastic container (my mold) then carefully add the other colour. Stir once or twice VERY carefully.

or alternatively...

5a. Wait for the plastic to gel (ie get to the stage where it is like jelly - or jello to Americans?) then mix the two together trying to create a swirl pattern.

6. Put mold in jar and pull a vacuum.

7. When it has hardened, pull it out and cut it into blanks.


Cam

 

[JimGo]

Do you add the catalyst to both cups at the same time? You might try waiting to add it in the second cup.

I would be willing to bet that if you wait 'till the mixture is like jello (fairly firm, self-supporting), then you won't get much mixing at all, and you'll probably introduce a lot of air. If you're waiting for the first mixture to just begin to gell (similar consistency to jam/jelly), then you may get less air, though I would think that the thicker consistency would still tend to hold onto the air bubbles more. I wonder if a different pouring technique, such as a very slow pour though a pinhole in the bottom of the cup, and barely holding the cup over the first layer of resin might not help reduce the air bubbles.

I haven't tried actively mixing the two layers of resin together; are you having any luck getting the kinds of swirls you want? I don't see any pics in your album, which is disappointing; I'm curious to see what your blanks look like.

 

[CameronPotter]

I'll post some pics when I take them. I have been a little slack on that... [:I]

My success has been mixed, but my main goal was to avoid the bubbles for now.

I did have trouble getting much mixing, and now that you mention it, I was pretty vigorous at that stage - probably adding a lot of bubbles.

I think that what I was thinking of as "gelled" was probably not what other people were thinking of as gelled (as I read all the articles here I could find).

My present batch which is hardening as we speak (although I am busy tonight and I can't test it [!]) and I mixed them before they gelled at all. As I said, the colours simply blended over night, but there is still an interesting kind of pattern to the plastic. I will do a pen out of this and post a picture of a pen from each of my four batches together.

Maybe my next one might turn out jsut right. [] I am getting closer all the time.

Cam

 

[DCBluesman]

Ok, time for a little physics lesson. Pulling a vacuum to get rid of bubbles is not a good idea. The reduced pressure actually causes the bubbles to increase in size. That's why the resin casting sites advise pressurizing your resin. The air bubbles can be compressed quite a bit (think of scuba air tanks). There are products out there that will reduce the surfact tension of your resin and thus make it easier for the bubbles to come to the surface. Most of the places that sell PR carry something for this purpose.

 

[JimGo]

Good luck Cam!

 

[CameronPotter]

Trust me, I have no problem with physics.

I also have no problem with understanding that if the vacuum is outside the PR, the pressure on the PR surface will be reduced and the bubbles will thus be more likely to surface. That is why some sites recommend using a vacuum on your casting...

In fact, the best is a combination of the two, vacuum then pressurise, but I am not set up to do it in two stages.

Cam

 

[Skye]

Cam, I think his point is that if you're under vacuum and one of the bubbles doesnt surface, that bubble will be larger than without vacuum.

I would asume it also depends on the thickness of the material (how quickly will a bubble float to the top, if at all) and how fast it sets. If either of these two work against you, you're going to trap the bubbles in the PR while they're larger than normal. If we're talking water, then yeah, the bubbles will float right up. If we're talking cement, probably not.

Just something you may want to think about. People dont get 'the bends' for nothin.

 

[terrymiller]

Cameron are you getting the bubble from stirring the PR if so you may want to try and build something like this.

http://www.rodbuilding.org/photopost/showphoto.php/photo/1284/cat/508/page/5

This could be built by using a rotisserie motor and a larger cup the solution is used slowly rolled around incorporating the two parts together without putting bubbles into the solution.

Another tip may be to use a propane torch to heat the top surface. This is also used in fishing rod building to release bubbles in the epoxy coating. They pass the flame just slightly below the epoxy the heat thins the epoxy just enough to release the bubbles. For PR you may be able to pass the heat just above the surface not touching the PR as it is flammable.

 

[CameronPotter]

Thanks for the idea. Actually, I have a rumbler (a vibratory motor) which might do the trick. I had meant to try it out when I started, but forgot along the way.

As for heating it, I thought that the plastic cured with heat, thus, rather than thinning it, I thought that would harden it faster.

As for the large bubbles in the PR... I do understand where he is coming from, but all I am saying is that the vacuum should ideally pull the bubbles out, but I understand that if one is missed, it may appear larger than it would have otherwise. However, my bubbles don't seem to be big, but simply there.

I think that it is more to do with mixing it in the almost hard stage (which was silly when I think about it) - when vacuum nor pressure would affect it.

Cam

 

[CameronPotter]

The pen actually turned out beautifully, just looked dull from the outside of the casting.

I have posted it in Show off your Pens and my album.

Thanks for the help!

Cam

 

[CameronPotter]

Here are my latest pens.

The green one is a homebrew PR, the red and white one is store bought.

I think I have this thing down pat now. You should see the bubbles get pulled out by the vacuum though! [:0]

Cam

<br />

 

[gerryr]

Those look good, but please, do us all a favor and lose that background.[:0] Seriously, the bright color really detracts from the pens, plus, having a background that bright can, and generally will reflect enough color onto the pens to distort the pen color.

 

[CameronPotter]

Thanks Gerry.

I wouldn't have a clue about the photography of the pens. I was just looking for something that was matte. I'll keep that in mind for the future. I am aware that the photography is ordinary, but I didn't take any time setting it up and did it last night with the dining room light on etc...

[|)]

Cam

 

[terrymiller]

Hey Cam just to follow up the heat at first thins the solution then causes the Epoxy to cure. Not sure if it would work for the PR or not. The rodbuilders will even put the Epoxy in there shirt pocket to warm it up. This can also be produced by using a heat gun or hair dryer. When heated the solution becomes a little thicker than water.

 

[CameronPotter]

Yeah, the reaction also produces heat. I have thought about usig a hair dryer to speed it up, but my first trial over heated and cracked (too much hardener) and as they say, once bitten twice shy.

Thus, I let it do it itself and just wait and watch carefully. Still, the hairdryer may come out soon.

Cam