Fire polishing cast glass help!

[Sandera]

I wonder if anyone can help?

I've made a number of cast glass stones varying in size and thickness from about 3cm to 10cm diameter and between 1cm to 4 cm thick (edges thinner than the centre generally.

I've worked through the grits so the stones are quite smooth whilst retaining a hint of texture. I'm aiming for quite a high polish finish and I've used cerium oxide to try and bring up a shine but I'm not achieving quite the effect I was after. It's been suggested that I could fire polish them but I'm a bit worried about the annealing. First of all, has anyone tried to fire polish cast glass and, if you did, could you recommend how I control the annealing part?

If not I'll just have to keep persevering with the cerium oxide!

[Zeldazog]

What sort of glass is it?  How did you anneal when you did the casting? 

You can use the same annealing section, just a lower process temperature to fire polish, than to cast.


If it's Bullseye, they have lots of tip sheets on kiln casting, and I know one of them gives recommended annealing times for various thicknesses of glass.

They also do a tech-note "Heat & Glass" which gives the ranges within which you can fire polish.


HTH

[Sandera]

Thanks Dawn.

That's what I suspected so it's great to have it confirmed. I actually used the schedule for the pyramid cast (from Bullseye). I'll experiment with one stone and see how i get on.

Just as a matter of interest, other than firepolishing, do you have a favourite technique for polishing cast glass with irregular shapes and a bit of texture? I've seen regular shaped pieces that are finished to a very high gloss (absolutely clear) but perhaps my expectations are too high for what I want to do?

This commission has certainly moved me outside my comfort zone as I hadn't done any casting for ages and what I did didn't actually need any cold work so this is all new territory for me.

[Zeldazog]

I know some of the blown and cast pieces that you see with high shine and sharp edges are done by cold working.

I have done a couple of classes with a glass artist who used to work with a maker in Nottingham, and her job for him for a lot of the time was hours and hours and more hours of work at the polishing machines.

I am not a caster, so its not something that I have to deal with often.  I've now got a belt linisher, but so far haven't had chance to see if and how much of a gloss I can get with a few hours of machine polishing.

[firedinglass]

  The only hesitation I would have about fire polishing a cast piece  in a kiln , is that it is not so controllable as cold working.......

[qwirkyglass]

What kind of glass is it?

If it is a lead casting crystal i.e. gaffer glass then it could be acid polished which can bring your glass to a super dooper high shine. But this can be costly and has to be sent off to a commercial acid worker (there are some in the midlands that i have used in the past) but for this your glass must have 35% lead.
shows a couple of different acid effects

Alternatively, you actually need to add another step to your hand finishing. If you use a pumice solution, quite thick with pumice and a cork pad or really dense felt pad (we use a felt wheel on a lathe soaked in the pumice solution) and you work this pumice into the glass until it is nearly crystal clear, and then use the cerium you will get a better finish.

You can jump straight to cerium but it takes longer and if you find your grinding is uneven then you have wasted more time polishing.

Hope this makes sense

[Sandera]

I know some of the blown and cast pieces that you see with high shine and sharp edges are done by cold working.

I have done a couple of classes with a glass artist who used to work with a maker in Nottingham, and her job for him for a lot of the time was hours and hours and more hours of work at the polishing machines.

I am not a caster, so its not something that I have to deal with often.  I've now got a belt linisher, but so far haven't had chance to see if and how much of a gloss I can get with a few hours of machine polishing.

thanks Dawn
I've actually really enjoyed the challenge and do like the effects of cast glass so I think this may be a direction I go in. I'm terrified of making a costly mistake re buying equipment that doesn't do the job. I've tried the linishers at Sunderland Glass Centre but felt a bit uncomfortable using theirs as there was a small class of us using 2 linishers and a lap grinder and it felt wrong to 'hog' the machines so, whilst i got an idea of how they worked, i never really got the chance to see a proper end result. When you do have a go at getting a gloss will you let me know what the results are like? I'd be dead grateful.

[Sandera]

  The only hesitation I would have about fire polishing a cast piece  in a kiln , is that it is not so controllable as cold working.......

That's very true - but I might experiment on one of the stones that I'm not so happy with and see how I get on.

[Sandera]

What kind of glass is it?

If it is a lead casting crystal i.e. gaffer glass then it could be acid polished which can bring your glass to a super dooper high shine. But this can be costly and has to be sent off to a commercial acid worker (there are some in the midlands that i have used in the past) but for this your glass must have 35% lead.
shows a couple of different acid effects

Alternatively, you actually need to add another step to your hand finishing. If you use a pumice solution, quite thick with pumice and a cork pad or really dense felt pad (we use a felt wheel on a lathe soaked in the pumice solution) and you work this pumice into the glass until it is nearly crystal clear, and then use the cerium you will get a better finish.

You can jump straight to cerium but it takes longer and if you find your grinding is uneven then you have wasted more time polishing.

Hope this makes sense

Those ducks make my mouth water! The colour and finish are fabulous. Are they gaffer glass and do you send them off to get them shined (shone) up? I haven't worked with lead glass before but hey i'm on a learning curve already so I may as well introduce a new dimension - if i don't try these things out now i probably never will.

Re pumice solution - I did read about this but i couldn't track any down (I didn't try too hard tbh). I did manage to locate a cork pad though. Oh and you are right about the polishing showing up scratch marks - 

[qwirkyglass]

Hi, yes they are gaffer casting crystal, i made them at the end of a project in uni, so managed to buy everyones left over crystal for cheap, hense so many colours
I love working with casting crystal, and i have tried bullseye casting billets too, but i find that gaffer is soo much softer it behaves better, melts more evenly and can pick up even super fine details, where as i found bullseye a little hit and miss. But thats my experience.
Yes they were sent off to be Acid polished, somewhere near dudley, but i also have a theory that a long bath in Etch all might work the same, but i have not yet had occasion to try it as i am stuggling to sell my existing ducks, so am not making any more right now.

As for the scratches, can i ask how you are judging when it is time to move to the next grit grade? and which grade grits are you using?
We were taught in uni that a really good way of telling is to get a good quality permenate marker, colour in the surface that you want to polish, leave to dry so that edge is now totally black, then start working with the grit. One every trace of black has been ground back, not just washed off, then its time to start again and move up a grit. You must also be super careful of cross contamiation as this is a bugger, one piece of grit can wreck a days work, i have many friends who found this the hard way.

For the pumice, you want the white pumice powder, which you then just mix with tap water and work with it that way
https://www.etsy.com/uk/search?q=pumice%20powder&view_type=gallery&ship_to=GB just a quick serch on etsy for you.

As for fire polishing i would be really careful, i could be done, but to get the high shine you have to take the glass to the point it is becoming liquid again and deforming, everytime i have tried this i have ended up with my piece slumped or a puddle. But if your really cautious you might have more luck than me, it might also work better as its not gaffer. but you still have to take it to the critical point.
Test with one piece maybe and makesure your shelf it really well protected.

Ok, ill stop rambling now. Good Luck
Hope this helps, and its all only my experience, someone else might have had more luck and have better advice

[Zeldazog]

As for fire polishing i would be really careful, i could be done, but to get the high shine you have to take the glass to the point it is becoming liquid again and deforming, everytime i have tried this i have ended up with my piece slumped or a puddle. But if your really cautious you might have more luck than me, it might also work better as its not gaffer. but you still have to take it to the critical point.
Test with one piece maybe and makesure your shelf it really well protected.

Thanks for this - I had typed it in my original reply about fire polishing being a higher temperature than slumping, but I see it's not there! 

Slumping is in fact the lowest process temperature of all kiln work (not classing annealing as a process), so yes, you have to be very careful if you're going above slumping temperatures as to achieve the fire polish you are making the glass soft enough to move .

[Sandera]

I'm really dim sometimes. Thanks for the reminder. We were taught the right way to move through the grades but guess who completely forgot and, in my haste, just ploughed through with no markers! Hence I'm going to have to go right back to the beginning and start again - from scratch!! Luckily I don't mind learning from my mistakes - I've had plenty of practice 
Thanks also for the pumice link - I've ordered some now. I think I may have to have a go at gaffer following your observations.

Re fire polishing - I'm a bit nervous but I think i'll give it a go just for the sake of experimentation. I'm mostly worried about the annealing but I think, as suggested that I'll use the original annealing schedule for casting glass.

Another thing though - did you find any problems with solution getting stuck in the textured places? After the cerium polish I have bits of the polish stuck in hairline surface cracks of the glass that I can't seem to soak out. There's always something!

[qwirkyglass]

Your toothbrush and some gental soap can be your best cleaning friend

[Sandera]

Your toothbrush and some gental soap can be your best cleaning friend

Oh that sounds nice and low tech! Thanks.