What is Fire polishing

[Ian]

Fire Polishing is done when you need to remove any blemishes from the surface of a fused blank of glass before it is slumped or processed further
It is acheived by firing the glass to a temp that just gets the surface to move slightly so that it levels off and smooths out leaving a nice glossy surface.
This temp is between fusing and slumping temp.
Ian

[nansea121]

About what temperature is good to do a fire polish at? Between 1225F to 1325F? (662.8C to 718.3C)?

[Ian]

Good Question Nancy
I will make up a table of firing ranges for the various firing temps so that one has a reference point to start from and then apply it to your particular kiln through observation to find the right temp for your particular kiln. I would say that you are right from 1225f to 1350f. Start looking at about 1200f and then keep checking until you have a nice polish and note the temp and how long it took to get to your desired result. Then next time you will be able to set your programme to go to that temp and hold time to achieve a fire polish

Regards
Ian

[nansea121]

Thanks:)

[ct4mom]

Thanks for asking this Nancy, I was going to also it was a little confusing on when and how to use this as well.

[Stephen Richard]

You can get a good overview of what happens to glass at various temperatures from:
http://www.bullseyeglass.com/pdf/technotes_tipsheets/TechNotes_04.pdf
you will see they suggest the range is 677C to 732C.  If you have sandblasted your piece, you can give it a satin matte finish by firing in the range 630C- 675C

[Stephen Richard]

Fire Polishing is done when you need to remove any blemishes from the surface of a fused blank of glass before it is slumped or processed further.

Sometimes you can add a devitrification agent, if you are unable to clean off all the devit with sanding or sandblasting.  This will work at the higher end of the fire polish range.

It is acheived by firing the glass to a temp that just gets the surface to move slightly so that it levels off and smooths out leaving a nice glossy surface.
This temp is between fusing and slumping temp.
Ian

[Ian]

stephen
when you say devitrification agent do you mean like borax spray
Ian

[Stephen Richard]

Yse. There are also a number of propriatary formulations too.

[Judy K]

.... Start looking at about 1200f and then keep checking until you have a nice polish and note the temp and how long it took to get to your desired result. Then next time you will be able to set your programme to go to that temp and hold time to achieve a fire polish....

I have found different glass has different temps. If I am making something from one sheet of regular art glass it may be harder or softer glass. I find 1380F will give me nice results for most glass types, without changing any surface texture I am trying to form with layers of glass.