First time PR casting, now comes the questions!

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Tieflyer

Tieflyer

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Jan 3, 2013
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171
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St. Louis
I made my first try at PR casting Sunday. Got the kit from CSUSA, prewarmed my resin in a hot water bath like recommended here, added 4 MEKP drops per ounce as per the temp chart included with my kit, mixed until I assumed it was mixed enough...need more instruction here, mine turned slightly greeninsh. Is that how you know it's mixed? Poured slowly, was very diligent with bubble removal. Two hours later it still hadn't flashed to gel Instructions indicated this should happen at 20 minutes or so. At this point I check humidity, it was at 74%, jumped back online and found a suggestion to park the mold under a 100 watt bulb. Did that and it finally flashed over. At the micro second it flashed though, a huge bubble released from the tube. Not sure anything is ruined as I'm just now feeling it has set enough to turn (it's Tuesday).
To those in the know...do I simply need more MEKP per ounce? I don't have any pressure or vacuum setup. Thanks!
 
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Hi Jeff - Some things I've observed while casting Silmar 41 / 249:

- MEKP will get "old" and lose it's effectiveness over time. Especially if stored somewhere warm. (I keep mine in a shop fridge). It can generally still be used, but it requires more than when it is fresh. If it won't cure acceptably with twice the normal amount of MEKP, I won't use that batch of MEKP anymore.

- "old" PR Casting Resin can have a greenish tint, especially after mixing with the MEKP. It should cure clear and still be useable.

To me, green resin and having to boost MEKP in a newly purchased batch of PR Casting resin would be a signal to find a new supplier.

All the above is based on my experience with Silmar 41 and 249. It may or may not be completely relevant.

Ed
 
Mine turns slightly greenish and is clear when it cures. I generally stir it quite a lot, more than it probably needs. I usually use 6 to 8 drops per ounce. You want pretty big drops, tiny drops mean you'll need a LOT more of them. Don't skimp on the MEKP.

I hope the bubble turns off.:)
 
Fresh silmar 41 has a blue tint. The older it gets, the more it changes to a yellow. I've never really noticed it being green, but in all cases, it should be clear once it's cured. I will say that most of my casting has been for color casting of pen blanks, not tube on casting.

Old MEKP will generally result in setting up silmilar to what you describe. A way to test MEKP is to shake the sealed container. You should have bubbles remain on the surface for awhile. If they dissipate like if you shake a container of water, then one of the components has evaporated. I think It's the ethyl. I was told this from US Composits.
 
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Ed McDonnell said:
- MEKP will get "old" and lose it's effectiveness over time. Especially if stored somewhere warm. (I keep mine in a shop fridge). It can generally still be used, but it requires more than when it is fresh. If it won't cure acceptably with twice the normal amount of MEKP, I won't use that batch of MEKP anymore.

.....
Click to expand...

What's the timeframe? My Catalyst is 3 years old, stored on a shelf in the tin shed, I live in the tropics and it's fine (used it this week).
 
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Dai Sensei said:
What's the timeframe? My Catalyst is 3 years old, stored on a shelf in the tin shed, I live in the tropics and it's fine (used it this week).
Click to expand...

Hi Neil - I don't have a scientifically tested answer to your question and can only give anecdotal evidence.

I live in a close to tropical environment and work in a shop without air conditioning with lots of natural light (reflected and direct). My MEKP comes in translucent (pretty much clear) plastic squeeze bottles. When I first started casting I would just leave the bottle of MEKP on my casting bench. I had a couple cases where the MEKP lost it's effect before I finished the can of resin (around 6 months). Other turners in my area who had experienced the same thing advised me to keep my MEKP in my shop fridge. Since then I have not had a problem with my MEKP losing effect before finishing a can of resin.

Is it the colder temperature? Is it the fact that it's dark in the refrigerator and sunlight can't get to the MEKP? Don't know, but I do know that storing it in a shop fridge seems to work for myself and others in my area.

Ed
 
I wonder if it has more to do with the humidity. I have no problems storing the MEKP outside in the shed here, but normally the humidity is in the 1-3% range, and only goes up when we're having thunderstorm weather.

I can't store the resin in the shed for long periods of time, I had a can self harden from high temperatures, it turned into a semi solid rubbery block!
 
I ended up talking to the folks at Craft Supply and they were very helpful. Their kit will get a slight tint when you first mix in the MEKP. Methinks that should be included in the instructions. As it cures...heck, when it flashes over, it's back to clear. My issue was environmental vs the amount of MEKP I used. Bumped my secon and third casts to 5 drops per ounce plus one extra drop and things started working much better. Already posted a pic of my 2nd cast in the pen forum and will turn the third casting hopefully tomorrow. Next up is casting colored blanks...heading to the library now!
 
Ed McDonnell said:
Dai Sensei said:
What's the timeframe? My Catalyst is 3 years old, stored on a shelf in the tin shed, I live in the tropics and it's fine (used it this week).
Click to expand...

Hi Neil - I don't have a scientifically tested answer to your question and can only give anecdotal evidence.

I live in a close to tropical environment and work in a shop without air conditioning with lots of natural light (reflected and direct). My MEKP comes in translucent (pretty much clear) plastic squeeze bottles. When I first started casting I would just leave the bottle of MEKP on my casting bench. I had a couple cases where the MEKP lost it's effect before I finished the can of resin (around 6 months). Other turners in my area who had experienced the same thing advised me to keep my MEKP in my shop fridge. Since then I have not had a problem with my MEKP losing effect before finishing a can of resin.

Is it the colder temperature? Is it the fact that it's dark in the refrigerator and sunlight can't get to the MEKP? Don't know, but I do know that storing it in a shop fridge seems to work for myself and others in my area.

Ed
Click to expand...

Ah, mine comes in Black bottles, so perhaps light may be the issue. MY supplier also keeps it in a locker, not on a shelf.
 
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