Rocket Science, Elusive Crystals, Simmerstats that Stick, Learning from Failure!

For the last year or two I have been taking an armchair interest in the progress of SpaceX, the company that Elon Musk founded. I have been entertained, worried, and inspired by the extra-ordinary spectacle of test rockets, said to be the size of 12 story buildings, slowly ascending, then flipping over onto their sides and dropping in a controlled free fall, before relighting their engines, flipping back upright and attempting a landing. Several of these tests ended with a spectacular explosion, but Starship SN15 successfully achieved what looked completely impossible, it really was like an episode of Thunderbirds made real!

I find myself seeing all this through the lens of art, performance and public sculpture as well as science and engineering.  Yes, there are moral and environmental questions thrown up by this sort of activity, but I have to say that I find the way Elon Musk goes about overcoming problems of rocket science and engineering gives me a bit more heart and perseverance when it comes to solving more humble problems of making and glazing pots!

As I reported in my previous blog post, I am having another go at crystalline glazes. The 23 February test that I did was really promising, with most of the test glazes producing crystals. I was therefore very enthusiastic about the next step in the process which was to glaze and fire some small vases and to see how the glazes worked on a slightly larger scale. 

I selected three of the most successful glazes from the tests and also made a modified version of one of them that I was hoping would give me nice nickel blue coloured crystals.

After glazing the first two vases I ran out of the zinc oxide that I had used when I made the glazes for the test pieces, and I switched to a supply of zinc that I had used in the distant past. Whilst this zinc had worked for crystalline glazes, I did remember that it had tended to be more of a vigorous flux in stoneware glazes than other zinc that I had used.

I applied the glazes more thickly than I did on the glaze test pieces. Crystalline glazes are very fluid at high temperatures and you have to allow for the fact that some of it will very likely flow off the pot.

After the pots were dry, I loaded the kiln and I fired it gently through the night so that it was at 700 degrees when I checked it at about 3.45am. From there I was able to put the kiln on full power and it reached peak temperature just after 7am. The kiln actually got to peak half an hour faster than I expected, and judging the peak temperature was made really difficult because of the bad behaviour of Cone 8 that decided to stay upright for longer than Cone 9 and the two stuck to each other as a result.

I think I may have a faulty box of Cones as I have had previous firings with Cone 8 not flopping fully even after cone 9 is down and 10 is bending slightly.

After the peak was reached I turned off the kiln, let the temperature fall to an indicated 1075, then restarted it. I kept the temperature below 1100 C for the first two hours of the hold, but then the kiln temperature rather mysteriously started to climb in spite of me reducing the power settings. This was odd behaviour, as a kiln will usually demand more and more power as the holding time ticks by because the heat that the kiln has stored slowly bleeds away. After battling the slow rise for half an hour, I surmised that one of the simmerstats may have stuck on a high setting and not be cycling on and off as it should. I turned both completely off and wound the knobs right round one or two times to see if I could free stuck contacts. Happily, when I restarted things, the simmerstats behaved normally again and I was able to bring the kiln back under full control. The temperature had climbed to 1125 whilst all this was going on, which was higher than I wanted.

I switched the kiln off after growing the crystals for about 4 and a half hours as I needed to grow the crystals about twice the size that I had grown them on the small test pieces in the previous firing where I had grown them for 2 and a half hours.

I was able to open the kiln the next day.....

The firing really didn't work out well at all, and of course this was a big disappointment, but it has been interesting and instructive having a good look at each piece and thinking about why the glazes behaved so differently from how they were in the test firing.

You won't see many crystals if you look at this group of pots, but the cone pack is rather interesting with cones 8 and 10 standing and 9 flat in between! On the front left is a rather brown looking vase with a blue crystal and some blue streaks, this was the Nickel blue crystal vase that I had high hopes for, but it came out with few crystals and really did look rather sad!

This white vase was marred by deep moon-like craters in the glaze. This was one of the stiffer feldspar based glazes. It really needed to be put on a little thinner and to have had a short hold at peak temperature to allow for the bubbles to pop and heal over. Whilst this glaze needed a bit more heat work at the peak temperature, it also shows signs of being held at too higher temperature when the crystals were growing, the scattering of crystal rods and occasional crosses are a characteristic of this.

The vase front right almost worked. This was one that had the same zinc oxide that I used in the tests... and it has turned out very similar to the tests! Annoyingly this had a bubble on the rim that formed a crater, so it is not as good looking as it might have been. Like the white vase with the craters, this one also may have benefited from a short hold at peak temperature to help the glaze smooth out.

This one almost worked, but....some tiny fragments fell into the glaze from the lid of the kiln whilst it was firing! Interestingly, the fragments acted as an irritant in the glaze that helped it produce crystals around them. If you look carefully you may notice that two of the crystals in the photo have little black dots in their middles.

 

Having had some failures to peer at.... 

I glazed more pots today and hope to fire again tomorrow!

Here is the kiln, all loaded and ready to fire again! I could only really fit these 4 vases in this time and a couple of testers. 

 

From Lessons Learned.... 

1) To avoid confusion I have got rid of  Cone 8 and will only use Cones 9 and 10 in this firing. 

2) When making these glazes I used some zinc from the same supplier from which I sourced the zinc that the February test glazes were made from.

3) I have applied the glazes slightly thinner than on the previous firing, and will aim to do a short hold at peak temperature to allow time for glaze to smooth over. 

4) I will aim to grow the crystals at about 1065 - 1075.

5) I will be alert for further simmerstat problems. 

Notes...

For anyone who is still here and likes looking at graphs, here is a comparison of the test firing with the firing of the vases. The 23 February test firing has a blue line joining the dots, and the  03 March firing has a red line.

The red line really shows very clearly the rise in temperature when I was having trouble with the simmerstats. At the time the temperature rise did not seem quite as bad, but I can see from this comparison that it subjected the glaze to a lot more heat work over the time the crystals were growing.

 

 "Failure is an option here. If things are not failing, you are not innovating enough." Elon Musk. (Source: Forbes, Quora, BrainyQuote, and numerous others)

NASASpaceflight has great coverage of the SpaceX rocket programme

https://www.youtube.com/@NASASpaceflight