I have played around with some different firing schedules. Quite time consuming. There are so many available on the internet. Here’s my results and think I have found something I’m kind of happy with.

 

First schedule was from a Facebook forum and as often is the case I had to convert the schedule from F to C. So this was my test schedule;

149/hr to 316 hold 15min to dry bottles

121/hr to 595 hold 20 min

204/hr to 787 hold 10 min

AFAP to 571 hold 45 min

10/hr to 382 hold 0 min   END

So the result was OK. The glass slumped to shape and the necks had closed. However, there were lots of spiky edges, which I believe probably meant that the temperature had gone too high. So for the next trial I decided to try a schedule with a lower top temperature.

So the next schedule used was the mould manufacturers schedule (I had not used this as had found other people using the same moulds who had said that the schedule doesn’t work and had suggested the one I tried (above) as working.

This schedule had a cooler top temperature:

260/hr to 82 hold 30 mins

260/hr to 593 hold 20 mins

93/hr to 732 hold 5 mins

AFAP to 549 hold 45 mins

66/hr to 371 hold 0   END

The feel of the resulting glass was very smooth and definately better than the first result in that way, but the neck bottles had failed to close and the bottom of the bottles were still too chunky and not melted enough for my taste.

My guess was that either I needed a higher top temperature and/or a longer hold at the top temperature or a slower and hotter ramp up. I looked at some other schedules and chose the glass campus bottle slump schedule, mainly because their flatten bottle schedule had worked well for me and my kiln. It also had a top temperature less than my first trial and more than the second. Unlike other schedules it also had a long hold at the top temperature (most other schedules for bottle slumping into molds have max 5 min hold at top, often it is 0 or couple of mins). The ramp up and down varies between schedules being around 535-595

So I largely used Glass campuses bottle schedule, just adding the bottle dry from the first schedule I tried (cos this sounds like a good idea and doesn’t seem to do any harm)

Schedule:

149/hr to 316 hold 15 mins

200/hr to 535 hold 20 mins

500/hr to 760 hold 30 mins

AFAP to 535 hold 60 mins

200/hr to 150 hold 0     END

 

The results of this I liked. Smooth, necks closed, no real obvious bubbles inside. My only question would be whether I could stop the curve in in the sides, but I’m guessing not, as even when I look at the lower temperature fuse of my second trial, this is the shape of the bottle coming out of the mould.

Comparing the first and third trials, the overall look and feel of the first is a lot chunkier. It seems to have more bumps in the glass and is less well defined. I could continue to experiment with ramp up temperatures and hold lengths, but as I was pretty happy with trial 3 , I decided to use the same schedule again on different moulds and with a heavier bottle in the split dish mould.

 

The fourth trial used the same schedule as the third.

The heavier bottle in the split mold came out a bit chunkier and with a few glass spikes. I guess I don’t want to increase the top temperature further , so one option may be to experiment with a higher temperature at the ramp up as per the first schedule ? The big dish worked out fine on this schedule. The candle holder dish did not work. This was left far too chunky and the bottle folding over ruins the use of it.  Therefore, I was happy with the basic dish slump, but I thought maybe try another method that I had read about for the candle holder. That would be to fully flatten the bottle first and then slump into the mould

For my fifth trial I played around with the schedule in that I removed the hold at the top temperature. My thinking was that the bottle was already ‘melted’, it needed only to ‘slump’ into the mould. I tried this out on both a thicker bottle in the split mould and a normal bottle in the candle mould. I reused a couple of bottles I had previously slumped flat (using glass campuses flatten bottle schedule). I then placed them in the kiln using the following schedule:

149/hr to 316 hold 15 mins

200/hr to 535 hold 20 mins

500/hr to 760 hold 0 mins

AFAP to 535 hold 60 mins

200/hr to 150 hold 0     END

 

 

I was quite happy with the results for the candle holder and think this is probably the only way to use the mould. The split dish worked fine also. The ‘shoulder’ bubble from the flattening however remains in the dish, so better reults are probably gained by just slumping a bottle (though depends what look you like at the bottom end, as in this version there is a far smoother end of the bottle and a more spacious dish space as the bottle end is less prominent).

I also placed a non flattened bottle into another split dish mould on the same firing just for curiosity of what effect the hold at the top temperature is having. The result was a slumped bottle with the neck still open – thus this confirms to me that the 30 min hold at the top of the schedule is needed in order to close the neck.

Thus I think now I have a schedule for flattening bottles (glass campus), a schedule for slumping into dish moulds (trial 3) and a schedule for slumping into the candle mould (flatten bottle schedule and then trial 5). Obviously some tweaking may need to be done around the schedules for different weights and colours of glass, but happy that I have some basics to start from.

 

Just because …….. I got a second hand mold from eBay, cleaned it up (with a washing up sponge and wet sandpaper) and kilnwashed it.

Strange mold as it seems too big for a beer bottle and too small for a wine bottle.

I wondered if I’d have to clean the mold each time and re-kiln wash. After checking information at Warm Glass for the kilnwash (using Bullseye kilnwash) this said that firings over 704 degrees Celsius would need to be cleaned off and re kiln washed. (Though other info suggests that molds need only be ‘touched up’ with kilnwash between firings – guess another thing to test). So I thought I would try a cooler schedule first to see if I could get away with a firing that would allow me to reuse the mold without repeatedly re- kiln washing.

I also tested drying the kiln shelf/ mold in the kiln (usually leave in kitchen for 24-48 hours) but took the kiln to 260 degrees for 20 mins (bung out) and just left to cool down as recommended on Warm Glass

I tried the slump float glass schedule on the KCR2 programmer as thiswent up to 700 as a high temp .

 

and got the following result:

The schedule was good enough to seal the bottle opening and left the bottle quite chunky. My feeling is that a hotter schedule is required.

I also put some other items into the kiln to see what would happen at this lower temperature to test a few other things:

  • tacking bottle glass (green bottle thinner than Bombay Saphire
  • whether pilot pens do indeed not burn off in the kiln
  • look of glassline paints on surface or between glass

 

 

My friend gave me a bag of empty Bombay Saphire bottles so I decided to test schedules for flattening these bottles and for flattening broken bottles for making into other items.

Before and after pictures below.

   

The schedule used worked well. This was the ‘wine bottle flatten’  glass campus firing schedule:

rate 200C to 535C hold 20 mins

rate 500C to 815C hold 30 mins

rate AFAP to 535C hold 60 mins

rate 200C to 150C hold 0 mins