Clear Casting Issues: What to do

Now that  fall is approaching, more people will be getting back into their shops to make some pens. Clear casting your own acrylic pens is very popular.

An issue that may occur when clear casting your own blanks is that the acrylic does not entirely cure. In other words the acrylic is tacky to the touch. This can be caused by a number of issues:
1) Did you use the correct amount of hardener per the manufacturer’s instructions?
2) Is the ambient temperature where you are casting, within the range of acceptable temperature for curing the resin?
3) Humidity – is your particular area very humid?

The best ambient temperature will be around 60-70 degrees. However, most of us do not live in that type of climate year around, so adjust the number of drops of hardening or curing agent for the ambient temperature as per the directions that came with your particular resin kit.

Resin casting tubes with fishing flies (left) and seahorses (right)

Resin casting tubes with fishing flies (left) and seahorses (right)

Finished seahorse resin casted pen.

Finished seahorses & shells resin casted pen.

If you did follow the instructions, and your cast was still tacky, a way to dry the acrylic is to place the mold in the direct path of the sun with a cover over it, and in about an hour it should dry, weather permitting.   Another option for drying is a toaster oven, but please do not cook the mold! Turn on the toaster oven (with your spouse’s permission, of course) to about 120° and once it is warm,  UNPLUG the oven, place the mold in the oven, close the door and let it cool down. This will definitely dry it quickly.

Now, I know someone out there will say “Then why can’t I just put the mold in the toaster oven to start with and accelerate the drying process?” Polyester resin needs a catalyst to get the reaction started, and when the catalyst is added, it generates heat. If you place the mold in an oven, you will only be generating more heat, and when the casting cools, it will be 10 times more brittle because you have heated it during the drying cycle! Polyester resin is brittle enough, without making it more brittle by overheating it.

I hope this will answer some questions about casting- we will delve into more casting issues in another blog entry.

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