I get asked a lot about what stones, fossils, bones and shells need to be sealed with a protective coating before putting it into the copper electroforming bath. Also, what is the best way to seal these things so they don't get etched, dissolve or contaminate our bath?
There are many products, materials and hacks out there for giving pieces a protective coating while it's electroforming and I've sifted through a bunch of content to find out what works best.
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Bones, Fossils, Shells, Leaves, Twigs, Acorns, Etc.
These types of material are very porous and it's likely the acid in the copper electroforming solution will etch the material and it'll not only dissolve but contaminate your bath, not fun. It's imperative that you take extreme caution when sealing these pieces.
First, make sure you clean your material. When it's covered in dirt it's harder to paint on your varnish. Take a regular old paintbrush and brush away as much dirt as you can. Then scrub it with soap and water. If it's super delicate like a leaf, just a simple paper towel damp with warm water will do. Gently wipe away dirt.
Now you're ready to seal your piece. Like I mentioned, they are more porous, so do around 3 coats of varnish, letting it cure in between each coating. Make sure there are no weak spots (spots that you missed when coating it) for the solution to seep in.
Let cure completely before adding epoxy or conductive paint.
Opals are probably the most tricky gemstone to protect from the acid solution bath, especially Welo opals which absorb water and any other liquid it comes in contact with, known as hydrophane. Australian and Mexican opals are a little more resilient but still need proper sealing for successful electroforming.
Much like the shells, bone and fossils you want to clear away any matrix (sand pockets) on your rough opal (if you're working with cabochons or freeforms that have been cut/polished then skip this step). I like to use a diamond bur grinder with my Dremel (or flex shaft) to take away unwanted material.
Once you're happy with the look of your opal it's time to seal the hell out of it! 3+ coats of your preferred varnish (list of protective sealants below). The best way I've found to seal them to make sure there are absolutely no weak spots is to do 3+ coats on one side, let dry and cure for 12 to 24 hours in between each coat (however long the varnish says it needs to be cured for) then flip it over and repeat on the other side.
You don't want to seal the whole thing at once, getting varnish all over your fingers then set it down on a spot you've coated because your fingers can create weak spots and certainly setting the opal down on a wet side will create a weak spot. This part needs to be flawless, practice your patients now because it's going to take a while and it'll be very tedious.
It's a general rule of thumb that anything below a 7 on the Mohs Hardness Scale should be sealed. But there's more to it than that. For example quartz is find to not be sealed but clear quartz has been known to get a blueish tint thanks to the copper electroforming solution being blue. So to prevent that you'd probably want to seal it.
I use lots of clear quartz in my jewelry and have never seen this happen, but there are a few folks this has happened to so to stay on the safe side seal your clear stones, not just quartz. Or, you can test it for yourself and if you feel comfortable not sealing then don't (I just need to add my disclaimers because I'd hate to tell someone it's OK to not seal and then they ruin a piece). =)
For crystal clusters it can be tricky to coat them without missing some spots in between the points. For stones like this it's best to use a protective sealant that you can dip the stone into, more on that later.
Misc; Plastic, Fabric, Glass, Pottery, Concrete, Etc.
For plastic you should certainly seal, 2 or 3 coats. Same steps as before, make sure it's clean, you can even take an alcohol pad to clean it down before sealing.
For fabric I would follow the advice I gave for fossils, leaves, shells, etc. I'm not too familiar with using fabric but you can electroform anything. Take a lot of care to seal it and paint with conductive paint. Obviously make sure the piece of fabric set in the position you want it to ultimately be in because once it's got a layer of copper over it it'll be hard to manipulate.
For glass you do not need to seal it. Glass is not very porous and will do just fine in the bath. This includes sea glass as well, you do not need to seal it.
For pottery, yes, you should definitely seal it. 2-3 coats. If it's very porous I would dip it.
For concrete, I haven't heard of anyone using concrete but it is very porous so I would definitely seal it, probably use a varnish you can dip the concrete in as to not miss any crevasses.
Other Types of Metal
All metal is conductive at different levels therefore all metal, that you do not want copper to form over, should absolutely be sealed. There are also many stones that have iron, copper and many other conductive metals in them. All should be sealed.
List of Protective Sealants
*Caution, never use a water-based sealant on hydrophane (Welo) opals.
- Clear nail polish - Favored by many
This is best used on opals and gemstones that don't have deep crevasses. Remove it with acetone (the kind you get from hardware stores, not from beauty supply store). Soak your piece in the acetone then take a toothbrush and scrub it away.
- Frisket (masking fluid) - Favored by many
Best used for mostly everything. For crystal clusters and any other super porous material, dip it in instead of painting it on. Easiest way to peel it off afterward is to first apply 3 coats so it's nice and thick. The thicker the coating the easier it is to peel off. Peel off while still wet.
- Mod Podge - Favored by many
Best used for just about everything. For crystal clusters and any other super porous material, dip it in instead of painting it on. The easiest way to peel it off afterward is to peel it straight out of the bath (rinse first) while it's still wet. Frisket and Mod Podge are neck in neck for being the most favored sealant, you just gotta try them and see which you like best for your own needs.
- Minwax Polyurethane
Best used for super porous, delicate material like seedpods, pine cones, leaves, etc. Best to dip your pieces in to get 100% coverage. This step happens before your conductive paint so you won't be needing to remove it.
Best used for sealing metal. Dip or spray it on, it's probably best to get the regular can, not the aerosol spray can (unless you think you'd be needing to spray it on more then dipping your piece in it) The regular can allows you to dip your piece in. This stuff easily peels off when you're finished.
Acetone is best used for removing any sealant that you can't peel off. Never remove the protective sealant after you use LOS or tumble/polish. Removing the sealant should be your very last step, but before applying your copper sealant, like ProtectaClear or Ren Wax, which in that case you generally don't want to get it on your stone.
I hope this guide was super helpful for you all. It's been a while since I wrote an in-depth article on electroforming. If you're curious about whether or not you should seal a material that I have not listed here just leave them in the comments rather than emailing me that way I can answer it publicly in case someone else is wondering the same thing. =)
I hope to cover sealing your copper jewelry AFTER electroforming to protect the finish. I also hope to write up an article about how to clean rough opal so it's ready for use in jewelry making.
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