Waterproofing craft porcelain?

October 9, 2007 11:51 AM

I'm trying to waterproof tiny objects made out of air-drying craft porcelain, but I've had little success. Suggestions for a translucent waterproofing material, or, perhaps, an alternate sculpting material?

Craft porcelain is perfect for what we're doing because it's translucent and doesn't need to be baked. The tiny objects (a touch wider than a pinky finger, but not quite as long) are being molded around a couple LEDs, so I don't think heating is an option.

They need to be waterproofed to such an extent that they can be submerged in liquid.

We've tried dipping them in polyurethane, spraying them with silicone, spraying them with clear acrylic, and dipping them in shellac.

It's possible that one of these methods would work but that our execution was imperfect. In each case the waterproofing would work for no more than a couple of hours, the porcelain eventually taking on water and growing bulbous and distended. It's possible that the craft porcelain is absorbing the waterproofing material over time. It's also possible that we're not waiting long enough between coats. (The polyurethane can says it's quick-dry, drying in a couple of hours, but maybe that's not to be trusted?).

Any ideas? Is one of those waterproofing materials worth trying again? Is there another translucent sculptable material that would waterproof better (and that doesn't require high heat to set)?

Our backup plan is to make molds and to pour the tiny objects out of silicone, but it would be much, much more convenient if we didn't have to go that route.

posted by nobody to media & arts (14 comments total)

polymer clay (fimo, sculpey, etc.) is easy to mold and shape and requires only 250-275 F to set permanently waterproof. most hard plastic won't melt at that temp--people cover bic pens in polymer clay all the time and bake them. that was my first thought. it comes in a rainbow of colors, including translucent. it can easily be sealed with a variety of materials, too, for a hard finish. it can't be used for objects that will touch food, though.
posted by hecho de la basura at 12:10 PM on October 9, 2007

Are you willing to have a fairly thick coating? If so, there are a number of clear epoxies that might work.
posted by aramaic at 12:21 PM on October 9, 2007

I use bowling alley wax for my iron work - if you don't want to heat the object before applying the wax, you can always heat the wax itself. Open a can, light it with a match (it's insanely flammable), wait for it to heat up the surface of the wax and then blow it out. Paint it on with a brush. It waterproofs well for objects that won't often be handled.
posted by Baby_Balrog at 1:08 PM on October 9, 2007

Is your polyurethane for outdoor use? How many layers of sealant are you using? Any little pinprick of exposed surface is going to be an issue, especially since anything that swells destroys the rest of the coating. I think you'll save yourself a million headaches by using a waterproof material in the first place.
posted by oneirodynia at 1:10 PM on October 9, 2007

Molding material, that is. BTW, shellac is not really very waterproof, especially in the presence of acids. I know some craft porcelain uses Sodium benzoate as a preservative, and it's only effective in acidic conditions.
posted by oneirodynia at 1:20 PM on October 9, 2007

Wow, thanks for the help so far.

Bowling alley wax sounds appealing, if it works. The objecs won't be handled at all, really, after being set up, but they will be fully submerged in water. Do you know if the wax will hold up/adhere?

(And how do I reconcile "light it with a match" with "it's insanely flammable"? I guess you mean that I should keep the match a healthy distance away but close enough to heat up the wax?)

And thanks for the polymer clay tip, hecho. I'll have to try a test run, but it looks like 250 F is just below the temperature limit for LEDs. (I'm also not sure if Fimo lets you sculpt with enough fine detail).

And aramaic: what would be a thin sort of clear epoxy to try out first?
posted by nobody at 1:35 PM on October 9, 2007

The best possible material for what you'd like to do is marine epoxy. You can get it thin enough to brush or dip. It seals surfaces incredibly well.
posted by fake at 1:40 PM on October 9, 2007

How long does it have to last? I don't think you'll find a 100% waterproof clear coating, it would be a woodworking holy grail. Shellac isn't even close, the water permeability is often a feature of it's use. Polyurethane is better but you'll want a solvent based product and you will still get transmission. Even marine epoxy is permeable enough to saturate the encapsulated contents if submerged in water; however you might get months of use before it becomes a problem. In building design the only 100% vapour barriers are metal and glass. Even water proof plastics like polyethylene will pass some water vapour.
posted by Mitheral at 3:42 PM on October 9, 2007

Fimo probably will hold some fine detail if you work at it. (Most people who use it don't have fine-detail skills).

You may want to try Future Floor Wax as a waterproofing agent; it is cheap and you can airbrush it on.

There's a number of two-part epoxy-type modeling compounds here, although have you thought of getting real porcelain, firing it, and gluing the LEDs in it?
posted by sebastienbailard at 3:44 PM on October 9, 2007

i second marine epoxy. because. you know. it's specifically made for the purpose of waterproofing things that are going to be fully submerged in water for long periods of time. that said, i would have thought that a few coats of polyurethane would have done the trick. but what do i know from craft porcelain?
posted by wreckingball at 4:15 PM on October 9, 2007

I've had luck waterproofing small electronic bits with crazy glue. Allow to cure overnight before submersion, though.
posted by porpoise at 4:43 PM on October 9, 2007

It sounds like Marine Epoxy is the way to go. Can anyone recommend a place to order from? (I assume regular hardware stores won't carry it?).
posted by nobody at 9:46 PM on October 9, 2007

If you don't have any local chandleries under "Boat Equipment & Supplies" in your yellow pages, just google "West System Epoxy" and go with a reputable online retailer.

Fun and related, although I didn't see any marine epoxy vendor:
http://www.kk.org/cooltools/archives/cat_materials.php
The "Magic-Sculp" looks like great stuff for small sculpures.
posted by sebastienbailard at 10:08 PM on October 10, 2007

I've used the bowling alley wax on lots of outdoor pieces, it holds up really well, rain or shine. Trick is, though, that you can scrape it off with your fingernails which is why it shouldn't be handled too much.

It is really flammable, but I was serious about lightin' that mofo on fire. Just the surface will burn, real big and bright, watch it, wait for the top few millimeters to melt, then put the lid back on to extinguish it. This allows you to have a little pool of melted wax in the middle of the can that you can apply with a brush. It's too stiff to apply cold, and you can't really heat your piece up anyway. Light it, let it burn for a second, cap it to extinguish it, and apply.
posted by Baby_Balrog at 2:06 PM on October 13, 2007