Coloidial Silica

What do you do with colloidal silica?

I should have been more clear. The colloidal silica is used as a coating for ceramic fiber to stabilize the fibers. If you use a gas-fired forge the fibers have a tendency to come loose during use. I'm certainly no expert, but I understnad that it's a health hazard.

The silica forms a glass-like layer that helps to seal in all the fiber-ey goodness (and keep it out of my lungs). The layer is pretty brittle, though, especially at heat. It's good to have some brick or kiln shelf on the bottom of your kiln to lay the metal down on.

This is my first forge, and I'm just begining this whole blacksmithing thing, so I'm certainly no expert... I'm just trying to share some of my experience with others. I'd certainly reccommend using the silica wash over any ceramic fiber... A couple of tips, though: Once the silica goes down it gets pretty crunchy. I thought I could spray some water on it to loosen it up a bit, but it doesn't seem to work that way. Once it's dry it's ridgid and pretty much staying in whatever shape it already has. In other words, don't coat the blanket, let it dry, and *then* try to form it with a little water. I've been brushing it on, but I think a cheap water-mister spray bottle would work better. The ceramic fiber crushes pretty easily, and a thin layer of silica breaks very easily, some times tearing a thin piece of blanket off with it. I think you're better off soaking the blanket. Also, I'd recommend using at *least* a two inch thick layer of blanket.

Just to share a little of what I learned building my forge...

First, let me qualify this by saying that it's far too easy (for me, at least) to get obsessed with the tools and not get a whole lot of work done, and you can easily do great work with just about *any* tools. So, if you're new to this, you shouldn't get too hung up on the exact forge design or anything, as long as it's safe and does what you want.

After I built the forge, I realize that I was a little too focused on the burners, and not the forge body. For a gas forge I think that, given the choice between a super-efficient burner or a well-insulated forge, it's better to have a well-insulated forge.

My thinking is that the working forge is analogous to a river flowing into a dam. The burner is like the river and the dam is like the forge. The amount of heat is like the level of water behind the dam. What you want is to get the level of water up as high as you can. No matter what, though, you're going to loose some water due to evaporation. If you open up the flood gates (i.e. loose a lot of heat) you're going to have to throw a lot more water in behind the dam to get the level to rise. If you close up the flood gates (i.e. insulate) you can have a relative *trickle* of water flowing in and the level will still rise.

Focusing on burners is like adding more water without closing the flood gates. You can do it, and it will work fine, but you're going to use a lot more fuel than you need to. I think most people will be better off with "O.K." burners and more insulation.

It's not a perfect analogy, but it should get the message across... Any comments?

As far as I can tell it just holds the fibers together.

I'm not sure of the boiling or melting temperatures... But with a little help from Google I get 3100=B0 F.

So that's at least the melting temp... If you can boil it in your forge you're way beyond me!

I don't think it does much to hold in the heat, either. It might make it a little worse, actually... It fills up the spaces between the ceramic fibers. This is just a guess, but I think it makes the insulation a little worse because the "air space" is filled with crystaline junk from the sillica. It's only for about 1/8", though, so it doesn't make much of a difference.

I should also say that colloidal silica seems to be commonly used in ceramics kilns. I decided to try it based on this thread:

OTOH, the risk from working with colloidal silica when you're applying it isn't small ! It's OK when it's wet, but if it dries out unbound and unfused, then it's one of the worst dust hazard materials you could encounter.

Thanks for the pointer, I'll keep that in mind.

I've only been using it wet, so I don't think there's too much of a hazard. The only time I have any sillica "dry" is when I scoop it from the package it came in into a big wide-mouth jar w/water in it.

I'll be more careful of the overspray when I apply the wet colloidal silica, too.

J P & all, Great to hear you have discoverd collodial silica. Glass blowers have been using it in furnace construction for years. it is a very versital material. Here are some other uses & tweaks for your forges using the stuff:

Mix your milled zircon with collodial silica instead of water, call this "Z-wash", this mix creates a much better bond to all surfaces,(blanket, brick,even steel!) brush it on everything inside your forge.

If you want a really durable forge interior get some "Satanite" or other high temp cement. First apply collodial silica to blanket insulation, let dry and then apply a thin 1/8" layer of Satanite and let it dry well. Follow this with a coat of Z-wash and you will have a very tough interior. You can still poke a hole in it but it's easy to repair. This should last about, forever.

Instead of hard brick for forge floors, get some ramable refractory clay. You can form this to any shape or thickness and when fired it becomes like hard firebrick. It still acts like a heat sink but instead a 2"brick you can have a 1/2-3/4" thick tough ass, flux resistant floor.

Another great material is "Castolite". This is a light weight castable refractory to use for doors, burner ports and I suppose floors as well. It is not as durable as ramable but much tougher than light firebrick. It does act as a heat sink but not so much as ramable or hard brick.

Don't nit pick to much, you can always crank up the psi. But it makes sense to spend a little more time at the front end of forge construction and then be able to work hard for years instead of months before relingning the thing.

Have fun, Glen G.

snipped-for-privacy@rgs.uci.edu wrote:

Hmmm... Memory is fuzzy here... it's sounding familiar, but it's been a _long_ time...

Is this colloidal silica the stuff used in the ceramic-shell-casting method?

Interesting stuff: