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09-24-2017, 11:01 AM
Third mold's the charm?
Though I got closer to a good mold last time, I also discovered the largest source of defects on my lenses. With the silicone caulk-in-soapy water method that I've been playing with thus far, the silicone is immersed. While this does help curing, water may also linger on the surface (where it is difficult to see against the translucent silicone). It wasn't air bubbles getting trapped in the mold, but water.
To address that, I decided to try one of the corn starch methods, which people here are likely familiar with as oogoo or proto-putty. There are lots of variants with various ratios of starch to silicone, some with thinners (to make it pourable), and some with colorants (like acrylic paint). I used the version at the second link, which uses food coloring.
The food coloring (being partly water) gets mixed into the silicone, helping it cure without needing as much humidity from the air. Obviously, it also colors the silicone. The corn starch fills a similar purpose as the dish soap did, keeping the silicone from being so damnably sticky (though I never quite got it totally non-sticky). It also absorbs any unmixed food coloring, preventing moisture from getting trapped between the mold and the part, and it allegedly helps with curing.
You just have to make sure to get a nice flat surface against the lens, and of course, make sure that you don't trap any air in the process. The food coloring helps both requirements by making the material opaque and colored, rendering the surfaces (and any possible crevices) easier to see.
The change in process paid off to a certain extent; my third mold -- the "Blue Mold" -- came out with about as good a surface as I could've hoped for without a pourable, degassed silicone. I put the master back in the cavity, shored up the bottom of the mold with additional silicone (the center of the lens was just a thin skin due to the too-small quantity of silicone I made the mold with originally), pressed the newly added silicone onto a piece of foam board to form a level base (being originally in the form of an upside-down rounded lump, it otherwise would've been hard to keep the mold level during pouring), and added a rim around the open face of the mold to contain any excess resin. Finally, I poured a new lens to test it out.
While waiting for that to cure, I decided to make an additional mold using this same process, primarily so I can cast two decent lenses at the same time. This one also turned out pretty well. I was shooting for orange, but ended up with a fleshy/meaty pink, which I will call the "Red Mold" (think Red/Blue stereo anaglyph glasses).
24 hours after the Blue Mold lens was poured, I demolded the part. I hoped that my more precise ratio would bring the cure time back to where it was with the first lens, but once again the part was slightly sticky on the silicone mating surfaces (not as much as last time, though). It picked up a slight texture from the uncured resin pulling away from the mold. I washed most of that off with isopropyl alcohol and then water, but some remained. Otherwise this would probably be the clearest lens yet.
By the time I demolded the blue lens, the Red mold had also been leveled and had cured, so I cleaned the blue mold of leftover resin (much easier than cleaning the lens, actually) and poured both molds. I also poured mold #2 from last time with the leftover resin of this batch. I had nothing better to use it on, and it'll bring the number of clear lenses I'll have to an even 6.
I'm not sure why my very first pour cured so much faster than the others, but I think that I'm just going to have to allow the full stated time for these latest parts to cure. That's fine; I really need to spend more time on my Halloween projects (all this mold making also gave me a few ideas).
As for my parts in post #30, it took more than 48 hours after pouring for the clear Treadwell lens to lose all tackiness. I still haven't sanded it. The dyed resin was worse; it didn't fully cure until around Friday. I could still bend the dyed Treadwell lens fairly easily until then. It is also cloudy due to moisture fogging (which is fine for that part, since it acts as a diffuser).
Though I got closer to a good mold last time, I also discovered the largest source of defects on my lenses. With the silicone caulk-in-soapy water method that I've been playing with thus far, the silicone is immersed. While this does help curing, water may also linger on the surface (where it is difficult to see against the translucent silicone). It wasn't air bubbles getting trapped in the mold, but water.
To address that, I decided to try one of the corn starch methods, which people here are likely familiar with as oogoo or proto-putty. There are lots of variants with various ratios of starch to silicone, some with thinners (to make it pourable), and some with colorants (like acrylic paint). I used the version at the second link, which uses food coloring.
The food coloring (being partly water) gets mixed into the silicone, helping it cure without needing as much humidity from the air. Obviously, it also colors the silicone. The corn starch fills a similar purpose as the dish soap did, keeping the silicone from being so damnably sticky (though I never quite got it totally non-sticky). It also absorbs any unmixed food coloring, preventing moisture from getting trapped between the mold and the part, and it allegedly helps with curing.
You just have to make sure to get a nice flat surface against the lens, and of course, make sure that you don't trap any air in the process. The food coloring helps both requirements by making the material opaque and colored, rendering the surfaces (and any possible crevices) easier to see.
The change in process paid off to a certain extent; my third mold -- the "Blue Mold" -- came out with about as good a surface as I could've hoped for without a pourable, degassed silicone. I put the master back in the cavity, shored up the bottom of the mold with additional silicone (the center of the lens was just a thin skin due to the too-small quantity of silicone I made the mold with originally), pressed the newly added silicone onto a piece of foam board to form a level base (being originally in the form of an upside-down rounded lump, it otherwise would've been hard to keep the mold level during pouring), and added a rim around the open face of the mold to contain any excess resin. Finally, I poured a new lens to test it out.
While waiting for that to cure, I decided to make an additional mold using this same process, primarily so I can cast two decent lenses at the same time. This one also turned out pretty well. I was shooting for orange, but ended up with a fleshy/meaty pink, which I will call the "Red Mold" (think Red/Blue stereo anaglyph glasses).
24 hours after the Blue Mold lens was poured, I demolded the part. I hoped that my more precise ratio would bring the cure time back to where it was with the first lens, but once again the part was slightly sticky on the silicone mating surfaces (not as much as last time, though). It picked up a slight texture from the uncured resin pulling away from the mold. I washed most of that off with isopropyl alcohol and then water, but some remained. Otherwise this would probably be the clearest lens yet.
By the time I demolded the blue lens, the Red mold had also been leveled and had cured, so I cleaned the blue mold of leftover resin (much easier than cleaning the lens, actually) and poured both molds. I also poured mold #2 from last time with the leftover resin of this batch. I had nothing better to use it on, and it'll bring the number of clear lenses I'll have to an even 6.
I'm not sure why my very first pour cured so much faster than the others, but I think that I'm just going to have to allow the full stated time for these latest parts to cure. That's fine; I really need to spend more time on my Halloween projects (all this mold making also gave me a few ideas).
As for my parts in post #30, it took more than 48 hours after pouring for the clear Treadwell lens to lose all tackiness. I still haven't sanded it. The dyed resin was worse; it didn't fully cure until around Friday. I could still bend the dyed Treadwell lens fairly easily until then. It is also cloudy due to moisture fogging (which is fine for that part, since it acts as a diffuser).