Steel moulds, whether stainless or other steel, require separators as glass will stick to hot metal.
The preparation of steel is a little different from ceramic or fibre moulds. First the steel has to have the oil coating removed. This can be done by sanding, sandblasting or by heating to about 550C.
The separators can be just normal kiln wash, boron nitride, or fibre. When using kiln wash or boron nitride, the steel needs to be heated – about 200C should be enough. Too hot and the water will boil leaving gaps in the coating. If the metal is too cool, the kiln wash will drip. A little experimentation will be needed to find the right temperature for your purposes. Remove the mould from the kiln and brush or spray on the separator. Return to the kiln to heat up again and apply the separator again. Continue this until an even complete covering of the metal has been achieved. It does not have to be thick.
Fibre paper works best on cylinder or wave moulds with curves in one plane only. Bowl shapes lead to wrinkling of the fibre papers and marking of the glass with wrinkles. This applies to the Bullseye Thinfire too.
Just as on shelves and ceramic moulds and as long as you fire below 700C, you can use the coated mould over and over with no problems. Once you fire hotter than 700C, it is best to remove the old kiln wash and put a fresh coating on before firing again.
I think your blog posts are a very useful resource – my only criticism is that they tend to suggest a way of doing things rather than alternatives.
ReplyDeleteWith respect to the current post, perhaps you could have considered the question of surface abrasion to enhance the setting of the wash; or the use of a hot air source to dry the metal mould once coated rather than heating the metal, etc.
For your thoughts.
Regards
Gordon
Divine Glass Design
Canberra, Australia
Yes, you are probably right that I look at things from my viewpoint rather than including a number of alternatives. Sometimes that is because I don't think the alternatives are really acceptable. Other times, I simply have not considered the alternatives. So comments like yours are good correctives. Thanks for your input.
ReplyDeleteGood tips, Stephen, but I just have one thing to add. There are boron nitride sprays such as Slide Hi-Temp 1800 and MR-97 that can be applied to a cold stainless steel mold. They are more expensive than buying powder and mixing your own but they work well.
ReplyDeleteIt should be noted that if you use Boron Nitride spray on ceramic molds you cannot go back to kiln wash.
ReplyDeleteI agree, except you can clean off all the boron nitride (abrasive, or sandblaster) and start again from the bare metal.
ReplyDeleteGreat tips but sometimes I mix a 1:1 ratio of kilnwash and water and apply it directly onto the stainless steel mold without heating it. It works well and the kilnwash sticks just fine but I use a very soft brush to reduce any steak marks and I usually only use this technique when I know the glass will be slumped at a very low temperature and is not likely to pick up any texture marks from the mold. I can't remember who gave me this tip but works for me.
ReplyDeleteI sandblast the mould first then apply kilnwash/water mix and find this lasts several firings. Then you only need to recoat with kiln wash as required.
ReplyDeleteRecently I purchased Hi-Temp 1800. Gave a couple of coats to my new stainless mold (Fusion Headquarters). Did a slump at 1165.
ReplyDeleteThe yellow bowl had stripes of black crud imbedded into the glass.
Should I have prefired the mold you think to burn of grease?
Maybe not enough spray?
I can see the stripes on my mold as well. Hope it is not ruined. Really did not want to sandblast it. Love the smoothness of it.
I am not familiar with Hi-Temp 1800. The procedures for steel moulds are the same what ever release is used. Get rid of the manufacturing and shipping oils. This can be done by firing, sandblasting, sanding, acetone, etc. Although I fire all mine. Once the oils are gone the coating can begin.
ReplyDeleteI assume Fusion Headquarters is using high grade stainless. So all you need is to clean off the existing separator and remove the residues to a clean bright metal. Then coat it. It should not be thickly coated. All you need is an even thin layer of separator.