PR changing color during casting

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M

musicman

Member
Joined
Jun 24, 2019
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15
Location
Texas
Hey Penturners,
I recently attempted to cast a royal blue blank using Silmar 41, and 24 hours later, when I removed it from tube, it was purple. I tried again, with a new PVC pipe and the same result happened. I poured 2 ounces with 20 drops of mekp into a 3/4" diameter PVC pipe. (The label says 10 drops per ounce)The temperature was in the mid 90s, no rain. I sprayed stoner mold release about 15 minutes before pouring, which I have done many times in the past. I stirred the resin for ten minutes. I purchased the resin within the past month and I store it in an air conditioned room around 76 degrees. I have used PR from a local hobby store several times with no issues. Does anybody have any ideas of the problem? Any suggestions would be greatly appreciated.
 
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A couple things need to be answered. First that is alot of hardener. I use between 5 to 6 drops per ounce or else gets too brittle I found. Did you warm the resin before you added color?? I like to do that and then add color and stir it in well. I then put back in toaster oven for another 4 to 5 minutes and add hardener. This way no bubbles. You should not have to use a release agent with Silmar. Silmar shrinks when it gets done.What type of colorant did you use and a photo would help. I found many blues look purple and tough to control. What color was the PVC pipe?? Maybe there was some contaminants inside the pipe when it was made. What you should try is make a sample in a clear resin rated plastic cup and see how it turns out. Did you cut through the blank andt was it a consistent color purple throughout?? If so then it is your dye may not be compatible to poly resin. If you are using alumilite dyes they do not work well. It is nothing to do with resin and temp. It has to do with the dye. That is my opinion.
 
Did you try turning it down a bit? I have had blanks look like they transitioned away from the base color only to find it was some sort of surface thing and it was fine underneath.
 
I used alumilite's blue and white. The pvc pipe is white. The first blank was purple all the way through. I have not messed with the second yet. I had a feeling it was the dye. As I mentioned in my previous post, this is my first time using silmar 41 so I'm still trying to figure out the do's and don'ts. Thanks for replying.
 
I have experienced color changes when using Alumilite dyes (formulated for urethane) with polyurethane (Silmar 41). I have also experienced foaming and color changes when using pigments for polyurethane in urethane resin (Alumilite Clear). So, I don't mix them. I use PR pigments for PR and Alumilite dyes with Alumilite.

Colors do sometimes shift with Alumilite resins (particularly Alumilite White), but my colors always stay true in PR.

I hope that helps,
Eric
 
Silmar can be tricky in keeping color separation. Because it's a longer curing resin, it gives the resin time for the 2 dyed resin to mix with each other, creating a new color. You have to wait for the resin to react /warm up and get thicker, before you pour. Also, vertical casting with PR will allow your colors to mix easier because it's all on top of each other, If poured too early. Lastly, like JT said, cut back on the MEKP to 3-4 drops per ounce. You don't want it too hot or your blanks will be very hard to successfully turn. Don't give up. You'll get the feel for it. It just takes a little time and practice. Alumilite is ideal for color pours in keeping better color separation, but you will need a pressure tank and I would recommend silicone molds for an easier experience.
 
What dye brands do you recommend for polyester resin? Can acrylic paint from a local hobby store work?
 
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