rigidizing fiber blanket

[Karyn Cott]

I think I was given some bum advice. I needed to make a mold that was 7" x 24" for a special order piece. All it needed to be was like a long and narrow sushi plate. I just needed a slight up-curve on the ends. I was told to get thick fiber blanket and soak it with rigidizer and let it dry and viola, a great mold. Well, to make a long story short, it still is not dry. My husband, the darling that he is, made me a wood mold (so the curved ends would be exactly the same) and topped it with aluminum foil so the hardener would not soak into the wood, since I could not put the wood mold in the kiln, dah....I have a hot fan blowing on this blanket. Any ideas on how long this is going to take to dry? The client needs this by Christmas.

[Bert Weiss]

Water is the liquid involved. Heat the mold hot enough for the water to evaporate. The stuff is not particularly shape stable though. Colloidal silica rigidizer sticks to glass, so must be well coated with kiln wash.

Personally I never bother to rigidize fiber blanket. I would use something like more fiber or sand to prop up the curved the ends. I simply dust the blanket with alumina hydrate and fire away. You are going to need something pretty stable to support the ends of the glass while flat. You can use brick or kiln shelf slices or whatever you have that is easy to draft in to use.

[Karyn Cott]

Thank you Bert; I had thought of using sand for the entire mold but my "techie" said sand would not work. I have casted onto sand before and loved the results. I will take your advice and prop up the mold with bricks or sand to dry it in the kiln and leave it that way when I slump the long piece on the mold. I know that when I have a question, I should always come to the board, but sometimes I just get in too big of a hurry and end up asking the wrong person for advice. Once again, many, many thanks.

K

[Morganica]

The only thing completely drying the rigidizer buys you (in my experience) is that it doesn't stink quite so much during burnout. And I've never seen a fiber rigidizer that didn't require a firing to harden. I'm sure there are some that work that way, just haven't had experience with one. Mine don't get hard until above 1100F, so a hot fan isn't going to work.

I do agree with Bert, though--rigidizing is probably more of a pain than it's worth unless you need an unusual, repeatable shape for many firings.

[Bert Weiss]

I've worked with wet felts (essentially rigidized blankets). You wet them, form them , dry them, then fire them. At the dry stage they do harden up, but at this point if you don't like the way the shape came out, you can wet it again and change the shape. After the hot firing it is stable, until you break it.

There are many creative ways to go about mold making. I have cut fiber boards in to shaped ribs and covered them with blanket. You have options to slump in or drape over. Each require different structure and firing schedules.

I agree that the sand might be tough to support the ends of a slump in mold. However it is probably fine to define the curved part. You will have to have a sand mix with a particle profile that holds it's shape. This means a variety of particle sizes. All small particles will not hold much shape.

[Karyn Cott]

Thanks for your input Cynthia; it is appreciated. Bert, sand does sound like a mess so perhaps just some extra rolled up fiber blanket will be enough to support the curved ends? What do you think?

K

[Bert Weiss]

Thanks for your input Cynthia; it is appreciated. Bert, sand does sound like a mess so perhaps just some extra rolled up fiber blanket will be enough to support the curved ends? What do you think?

K

Yes. If the shape is not perfectly defined, you don't want to fire too hot, as the glass will conform with what is there.

If you have thick blanket, you might try cutting pieces in the shape of the curve for each end. On the other hand, if your rigidized piece is pretty good, you will just need to support it as best you can.

You can make a putty by mixing fibers and rigidizer to smooth and stiffen the mold. I have limited experience with this. I patched a refractory cement mold with a putty I made with dust from vermiculite board and rigidizer. I made the dust by sanding the board with coarse sandpaper. You might try grinding up blanket fibers or sanding boards. My putty worked remarkably well on the cast mold. I plan to mess around with this idea more in the future.

[tonyroberts]

I do agree with Bert, though--rigidizing is probably more of a pain than it's worth unless you need an unusual, repeatable shape for many firings.

I've never rigidized at all, but have wondered about doing it to extend a mould's life. My fibre moulds last just one to three firing usually. If I rigidized the fibre, and supported the mould well on sand, how many more could I expect?

Tony

[Bert Weiss]

I do agree with Bert, though--rigidizing is probably more of a pain than it's worth unless you need an unusual, repeatable shape for many firings.

I've never rigidized at all, but have wondered about doing it to extend a mould's life. My fibre moulds last just one to three firing usually. If I rigidized the fibre, and supported the mould well on sand, how many more could I expect?

Tony

This is tough to answer because of the ease of breaking the mold from handling. It also depends on what sort of fibers you start out with. Papers are weak and blankets less weak. Then it depends on which rigidizer you use, silica or alumina. Silica rigidizer, the most common, requires kiln wash as the rigidized surface will stick.

[Brock]

A properly rigidized and KWed fiber mold can last for years. I had a torso mold for over 10 years. Because of their fragility it isbest to leave them on a dedicated shelf. They are fairly strong in a weight bearing sense, but can break with handling.