casting disaster!

[GaryPlaysWithDolls]

Tried casting a few heads tonight and let me just say AAARGG!

Didn't do it right, wound up ruining four heads. (They looked...not right.)

I didn't heat up the molds, I think my resin stuff is old and I mixed up too much and then hurried to pour it into other molds so as not to waste it.

[jessica]

That bites. Hate when that happens. Do you have to heat up your molds before a pour? And how much for how long?

Also were your molds good molds to begin with or was this the first time you tried/tested them?

[GaryPlaysWithDolls]

Yeah, the instructions say to heat them up (a step I often forget).

I actually had REALLY good luck with my first mold and cast. I noticed, though, as I've gone on, that my castings are just not coming out very well. I don't know if I'm not mixing it right or if my stuff is getting old (noticed that one of the resin ingredients is getting kind of, I don't know, crunchy around the edges. I'm afraid solid particles are getting in he mix. I was thinking about trying to strain it. I don't know. I'm bummed.

[jessica]

I only use the two part mold and cast mixes, but I don't remember it asking me to heat it up.

[Tothiro]

Warming the mold affects how the resin cures since it's a thermal reaction. Sometimes you might want a warm mold, sometimes it doesn't matter. I forget the science behind it honestly... I should go google that.
I usually don't heat them myself, but on occasion I will notice better pulls the second or third time I cast in a row because the last batch left the silicone warm.

G- Are your pulls getting bubbly, or foamy? Or are the skins just not as smooth on the cast? If it's the first it would sound like moisture in the resin, if it's the latter it may just be the mold getting old. Whenever you pop out a cast it wears on the surface texture a bit and after a relatively short number of casts it can get a little ragged.

The crusty bit is the resin getting damp by air exposure - and the resin definitely has a shelf-life. If you're not using resin very quickly you might pick up a can of X-Tend-It or something. It's a heavy gas that pushes air and moisture up out of the bottle if you're not regularly casting. Comes in bottles like the compressed air for cleaning pc keyboards and should run about 4 or 5 bucks.

Just don't huff it - you'd suffocate standing up.

[GaryPlaysWithDolls]

Thanks! Yeah, the casts are looking pretty foamy. Like swiss cheese. Tons of air bubbles in the top of the heads.

[jessica]

My friend told me never to shake the resin before mixing--just mix each part A and part B with their own dedicated sticks to avoid cross contamination.

[GaryPlaysWithDolls]

I'm not sure if I'm shaking it or not. The one chemical looks like it is separating. I strained it through pantyhose to get out any chunks/crystals.

I gotta admit, I'm bummed.

[jessica]

I have used resin that looked like that, and from what I remember, the casts took longer to fully cure (like days!) but I had no bubble problem.

[GaryPlaysWithDolls]

I've got more bubbles than a drowning asthmatic.

[Tothiro]

If it's foaming, that's moisture then. I'm afraid it sounds like the resin batch is toast... you might need to pick up new material.

Certain environmental things can also affect it, like humidity in the air when casting, or even temperature outside. Too much pigment will add moisture too if you're mixing in additives. Usually it's just the resin though.
If it's an unequal mix a/b type then your mix percentage measurements may be off too, and that would have a similar effect. If it's a straight-up 1:1 ratio mix i gotta go with old stuff.

[jessica]

I think Don also mentioned that he powders his molds before pouring resin, to help minimize bubble formation on the surface. Have you tried that?

[GaryPlaysWithDolls]

I just powdered my molds for the first time today and got better results than usual, but still so much air bubbles that it upsets me.

The stuff might just be old. I've had it for awhile and it sat in the garage for part of the winter. I hate to think (or tell my wife, that it might just be toast). I haven't had a good cast for quite awhile.

[ctc]

>I think Don also mentioned that he powders his molds before pouring resin

Yeah. It helps negate surface bubbles. Also; I got the mechanism out of one of these weird motorized Spirograph-kinda pens: it shakes when you turn it on.... I use that to vibrate the molds when I fill them so's to shake loose more air. If you're getting a lot of airbubbles, it could be old resin, like you suspect. Old stuff will also come out a slightly different colour than normal, and/or have a slick, oily feel from a poor catalytic reaction.

I've never heated a mold though. (They heat up from the resin curing though.) What's the deal with that?

Don C.

[GaryPlaysWithDolls]

Sounds like I got some old stuff. My brother-in-law mentioned the vibrating thing. That might be something to think about, too.

The alumilite instructions say to heat the mold in the oven. It gives no reason for this. I just follow instructions (poorly, but I try.)