Here are some of the wonderful information that was sent to me:
Joanie Berkwitz
Yes, this was a problem 'way back when'. Incompletely mixed resin, where the body and the catalyst hasn't completely fused. My guess it that it is catalyst that is leaking through minute veins of unconsolidated material. (it lies like a thin vein or ribbon running through the cured resin)
The yellowing is probably from the resin being exposed to UV light. It's an aging issue, not a smoking issue. I have resins in the workshop (reference material) that have never been near nicotine. Just like plastics and PVCs will degrade and become brittle from exposure to UV light, so will resins, particularly the older ones.
I poured resins, once upon a time. Pour Horse started out in the resin business. Hated the stuff and developed allergies to it. But the old resin didn't mix as completely. You would end up with, like I said, little fine ribbons of the catalyst (which is thinner and more liquid) running through the resin body. (body, in this case, meaning the actual bulk material that had to have the catalyst to cure) These little streamers of catalyst would remain oily, once the rest of the resin 'kicked off'. There is nothing left for the catalyst to react to. Remember, resin curing is a chemical bonding cure. A reaction cure. As opposed to drying, or being heated, or whatever
In the curing process (which takes only minutes, once the mix is started, up to maybe half an hour typically) heat is created. The heat is the energy being released by the chemical bonding action. The heat varies by type of resin... and also the brittleness or lack of brittleness is a property of the varying heat releases. The newer resins mix better, don't know what they did, but like Betty Crocker puts things into cake mix to make it mix easier, the resin companies must have done something similar. You don't come across that any more. No fix as far as I know, because nothing is going to draw that oily stuff out except capillary action over time. Even a strong primer can only hold it in, not cure it. Eventually it will work its way underneath and flake paint off.
The bottom line is that I never heard of one of these sticky guys being fixed fully, but it was fairly rare to find, and also that the yellowing (and stickiness) didn't have anything to do with smoking. Nicotine can definitely hurt resins and plastics, but not in this way....
A sprue is actually an outlet for air, it's not usually the term used for the pour hole. A sprue might go from the ear tips, tail tip, etc to the outside of the mold so that when you pour the resin in, the air can escape out and let that part fill all the way. I've always said 'pour hole', though resin casters might have a different term. In ceramic, there is also a 'spare' which is an additional piece that fits over the pour hole to make it longer, but resin casters don't use that.
Sprue holes would be much smaller, they are more like little tubes. I have used things like coffee stirrers imbedded in the claying up of the mold to create sprues, also heavy gauge wire. They only need to be big enough to let the air out, but they don't need to be too big or otherwise the resin will come out and leak all over everything. There is a book on the ancient bronze horses of San Marco that talks about their sprues. A very old technique! Bronze is even more viscous than resin, so a bronze casting would have a lot more sprues so that the air can escape and let the bronze in quickly. Otherwise, legs and stuff are like a straw that you put your finger on the end of, and put it in your soda... the straw won't fill with soda until you take your finger off. Same principle. In ceramic, however, the air can go between the edges of the plaster mold (which are never a perfect fit) and also into the pores of the plaster, so ceramic molds don't need sprues.
Sheila Bishop
Joanie is right. It's sometimes caused too if the resin is old or it's being used in a hot area, it kicks too fast and causes the same problem. Also some of the resins can be cooled to make them kick slower but it can also keep them from chemically bonding. Some are very sensitive to cool temps. Normally if it's leaching all over it's a done deal.
Sheila Bishop :
They do sometimes leak from the spru. It's not common if it's all over the horse so it's not a good sign when it's doing this. There are many things that can make it happen. Not drilling a vent hole after casting, resin not mixed well, being exposed to heat (most common cause of oil leaching, especially in older resin), not enough or too much mold release, stripping will do it (resin is very chemical sensitive) and so on.
Try to drill a decent size hole in the resin around the worst area. If there is uncured resin still inside, it can cause that oily stuff to surface. Make sure you clean out any resin goo you find (if any). If that doesn't work drill a few small holes in the oily areas. Let the horse sit in a hot area (not direct sun but outside where it's hot). It will help bring out any oil. Leave it a few days, bring it in, clean it with alcohol and do it again, until it stops. If you get it to stop give it a dry baking soda bath, then clean with comet and hot water. Let it sit in a warm area again. If still clean then fill all but one vent hole and primer. If you use Painter's Touch primer (at Home Depot) it helps since it's made to stick to plastic. Good luck.
Wonderful information ladies thank you so very much!!!
In my case with this resin is that the oily stickies are in many places.....I am very glad that the customer and I decided to alleviate all possible causes by removing all paint, primer, and fillers and starting over from scratch and starting off with using a different primer for the second go round. I am very thankful that the resin had not been shipped to the customer and then developed its issues....
The newer made resins that are shipped to me are light in weight and the surface is very smooth. Some have the texture and feel of fine white marble. I have one older resin here that, before I had her prepped, reminded me of very dark matte antique glass...a fantastic blackish-green volcanic matte glass look and wonderful feel.
I hope my posting my resin event...and the info I received from Joanie and Sheila will be helpful to those who also may have this issue arise.
Have a wonderful day everyone!
C.S.Richmond Studios
Sheila, by drilling vent holes, are you talking about doing it in hollow castings? If they have air pressure built up inside, does that force leaching? Interesting.
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