Problem casting PR ribbons

ribanett · Sep 2, 2010

This is the first time I have tried to cast PR ribbons.

I cast two blocks and both of them broke. The breaks are clean between the ribbon and the clear PR.

I used Castin'Craft Clear and PearlEx Brilliant Gold for these blocks.

The ribbon was made from a 10 to 1 ratio of clear to PearlEx with 20 drops of MEKP per oz. and poured onto plate glass. I waited until the pour was not sticky to the finger before cutting into strips and folding into the mold.

The clear/MEKP mix was 4 drops per oz.

Thanks for any help in advance.

Craftdiggity · Sep 2, 2010

Larry,

So if I am understanding you correctly, the ribbons themselves are PR? If that is the case, my only thought is that your resin is poor quality, because resin to resin should be strong. I've only worked with Simlar so I don't know about the CC resin, but I've never had a problem like the one you're describing. It's a really cool idea by the way. I like the look. I bet you could get pretty close to a cactus look if you wanted to. I might have to try this out.

ribanett · Sep 2, 2010

Craftdiggity said:
Larry,

So if I am understanding you correctly, the ribbons themselves are PR? If that is the case, my only thought is that your resin is poor quality, because resin to resin should be strong.

Chris

The ribbons are made out of PR. Both the clear and the ribbons came from the same can. The only difference is the PearlEx. I am wondering if the powder is preventing the bond.

gothycdesigns · Sep 2, 2010

I could be wrong, but I thought I read about making ribbons, was best that the ribbons were still tacky. not quite cured, but soft enough that when you cut the strips and it'll be the ribbon.

grub32 i think has a good video showing how he makes his ribbons, and mentioned they should be tacky and when cut should move right into pouring your other PR. That way they should cure together since being from a different. He has a few vis on youtube.

http://www.youtube.com/user/grub32?blend=2&ob=1#p/u/16/GMKurStoGPc

Brooks803 · Sep 2, 2010

the PR should bond to itself nicely even if the ribbons were cured. Did you cast the final blank under pressure? If not there could have been a buildup of air bubbles on that seam where it broke since theres just that small gap between the ribbons. That could have weakened the resins structure. If thats not it....i have no idea.

PTownSubbie · Sep 2, 2010

The weak joint is the ribbon to block location. I have always had problems with this interface.

Try to sand the ribbon lightly prior to casting. It will give more adhesion.

Use really light cuts and thin CA as protection.

truckfixr · Sep 2, 2010

What did you use to clean the glass you poured your ribbons onto? If the cleaner you used left behind any kind of residue, it would be on the ribbons and could prevent adhesion.

ribanett · Sep 3, 2010

Thanks for all the help.

In the photo above you can see that the split-line is slick and glossy. It looks the same as if a crystal was cleaved except it follows the ribbon line. Looked at the surface under a 10X loop. There is no clear PR on the ribbon.

I made a ribbon from clear PR and made two casts using clear PR as a filler. The first one was made when the ribbon was soft but not sticky to the touch. The second cast was made after the ribbon had time to fully setup. Both cast have perfect bonding between the two surfaces.

The problem looks to be with the PearlEx I used as a colorant.

Tonight I am going to give it another shot using artist oil-color. Will post the results.

Thanks again.

DozerMite · Sep 3, 2010

It looks like it came apart where there were two ribbons side-by-side. There isn't much resin that got between the ribbons. That coupled with the different amounts of catalyst can create a weak point. The ribbons might have cured faster than the rest and pulled away from the clear resin since there was such a small amount between them. I haven't had one seperate like that, so this is just one possibility.

Either use the same amount of catalyst for both the ribbons and the cast or let the ribbons cure (the way I do it) and then cast them. Just my two lincolns.

PenMan1 · Sep 7, 2010

Larry:
If you are pouring your ribbons on "glass", make sure that it is glass (with no tinting,etc), not plexiglass. I had an issue once with a tinted picture frame glass. Apparently, the PR didn't like the chemical used to tint the glass. If plexiglass is used as an underlay for the ribbon, the heat from PR casting causes a reaction with plexiglass.

Next, if you use Windex or other ammonia based cleaner to clean the glass, make sure to rinse it completely with water. PR doesn't really like ammonia either. Then make sure to dry the glass completely with paper towel (PR hates water, too).

Lastly, I use 9 drops of MEPK per ounce on ribbons and 5 drops per ounce on 3/4 blanks. I have also found this to somewhat more problematic in high heat and humidity (Georgia Summers!) than during winter.

I did find that not removing the residual windex from my ribbon glass was causing most of my ribbon separation problems.

Good luck!

capcrnch · Sep 7, 2010

Brooks803 said:
Did you cast the final blank under pressure?

^This

I had this exact thing happen, until I used a pressure pot.
Only then did I stop the cracking.

I wish I still had the pictures, but it was the EXACT crack yours had. My block was a different color, but it looks like deja vu!

Problem casting PR ribbons

ribanett

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