Casting With Water-Clear Resins
This was a fun little project inspired by a Poly Optic resin piece I saw in an old Polytek mold manual. The description in the manual didn't really offer instructions, but from what I could gather, the hand print was made with PolyOptic 1411 and PlatSil 71-10 silicone.
So the other night I set out to make my own version of this sculpture. To begin, I molded my hand with Accucast 590 palm down on a board. Since I really didn't need the back of the hand I just focused on getting a good palm print. Once the Accucast mold was cured, I removed my hand and poured in PlatSil 71-10. I chose 71-10 because it doesn't need to be degassed and it cures in 30 minutes.
Once the 71-10 silicone hand print had cured, I trimmed it up and built a foam core box just slightly larger than the hand print. I actually did two attempts at the Accucast hand print. Pictured above is my first try. I wasn't happy with it and didn't really want the wrist included so I did it again but didn't photograph it.
Once the foam core box was assembled I glued it together with Hot Glue and then rounded the inside corners with Protolina Grey-Green clay. I rounded the corners to give the piece a little more stylized look. Also, Clear resin seems to cast better in forms with rounded edges. Sharp corners sometimes look funky if the resin cures fast and shrinks back slightly.
After the clay was in place, I mixed up another batch of PlatSil 71-10 and poured it into the bottom of the box about 1/8 deep. I used a chip brush to brush the silicone up onto the box walls and then left it alone to self level. This step allowed me to easily create a glossy surface all over the inside of the box. Before the silicone set, I carefully placed the hand print into the mold box so it would bond to the puddle of silicone in the bottom of the box.
I allowed the 71-10 silicone to cure for 30 minutes and then I was ready to pour my Poly Optic casting resin. For this part, I didn't vacuum degass or pressure cast the resin.
Some important points to remember when working with PolyOptic or Water Clear resins:
- Clear resins are VERY sensitive to moisture. Work in a climate controlled are for consistent results.
- Stir with a steel spatula rather than a wooden stir stick to minimize the chance of moisture contamination. Be sure to also use a clean mixing bucket that is plastic rather than paper.
- Remember that Aliphatic clears (such as 1411 or WC-786) cure from the thickest mass out. Thin areas may take up to 1 hour longer than the rest of the piece to cure.
- Thick parts will exhibit higher shrinkage than small thin parts. If you want lower shrinkage, use 14R retarder to slow down the cure.
- Small, thin parts will have troube curring if the cross section is under 1/4 inch. To offset this, the mold can be heated with a work light to ~100F-120F. This added heat will aid in curing the cast resin.
The finished cast, even with air bubbles, came out very nice. Had this been cast under pressure, it would have been flawless. That said, at present we don't have a pressure tank big enough for a part this size. One of the aspects of clear resin that is really captured in this type of piece is the role of texture in a piece. If you have a matte surface, your piece will not be water clear, but more like frosted glass. The purpose of sloshing the 71-10 around on the box walls and creating a self-leveling puddle is achieve a gloss surface everywhere except the hand. Remember that if you want absolutely bubble free parts, you will have to pressure cast you part. Clear parts with zero air bubbles are impossible achieve without pressure casting.
On the heels of that cast, I decided to take it a step further and I put the box back together and cast in EasyFlo 60 this time to get a plain, hard plastic pattern. My goal at this point was to make a permanent mold for multiple copies of this sculpture since the original foam core mold was really only suited for one or two copies.
The EasyFlo 60 pattern was then used to create yet another PlatSil 71-10 silicone mold The final mold will now allow us to make dozens of resin copies in a variety of materials. Pictured below is the finished mold along with three copies cast in our new WC-786 clear casting resin. Two of the copies have very small amounts of PolyColor pigment mixed in to give a subtle color effect.
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