Monday, October 2, 2017

Porcelain Paperweights. One important step remains... Hammer and Chisel!

A scary, but unavoidable, part of making a pot with a crystalline glaze is separating it from the little ring of porcelain and the glaze catching saucer. I was a bit anxious about the paperweights as their round shape does its best to deliver the maximum amount of run off glaze right to where the porcelain ring is joined onto the paperweight, and there was a chance that glaze would penetrate the join and glue everything together.

Some crystalline glazers favour using a gas burner with a very thin flame to work around the join, but I find that a sharp chisel and a hammer does the job quite well.

I like to tap right round the join quite gently and try to form a little scratch or fault line in the run off glaze with the chisel as I go. I can generally give a series of smart taps after this, and the ring will pop off.



 The run off glaze leaves a sharp edge and this needs to be ground off.

Wet grinding with an abrasive disk fitted to the wheel head is a great time saver.

I finish off around the edge by hand with a high tech sharpening "stone" that is designed for sharpening chisels.


The paperweights really come to life in sunlight. The crystals scintillate in spectacular fashion, and their intricate structures become more apparent.


  1 percent cobalt oxide gives both blue and purple in this glaze.

1.5 percent nickel oxide gives Prussian blue crystals and a orange glaze around them. Amazing details in this glaze, you could spend hours with a magnifying glass exploring the stars and flowers!

The star shapes in the centre of these crystalline structures are rather fine!

Copper carbonate with just a trace of iron oxide gives golden crystals floating on a green glaze.


A Crystalline glaze recipe

I have played with several crystalline glazes over the past few years, but the one I use most often at cone 9 - 10 with the porcelain clay that I have is as follows;

Frit 4110  47
Zinc oxide  27 (you can use regular zinc oxide, but you may find calcined zinc makes the glaze somewhat easier to apply).
Silica  24
China Clay 0.5
Bentonite  2

+ Titanium dioxide  3 (The titanium is left out altogether if nickel oxide is used for colour, but is part of most other glazes in 2 - 5 percent)

To this you can add copper, cobalt, iron, manganese, or nickel, by themselves or in mixtures with interesting results. Rutile and ilimenite also extend the range of possibilities. You should experiment. The glaze should be applied thickly.

The way that the kiln is fired makes a profound difference as to how crystalline glazes turn out. Temperature and time are used like an artist's paint brush to create crystals of different sizes and shapes.

A way to start with the glaze base I have given here would be to fire as follows.

Fire quickly to Cone 9 fully down and Cone 10 starting to bend --using cones-- not just relying on controllers and gadgets! If possible the kiln should climb at at least 125 Celsius (257 F) per hour for the last hour or two (more is better). Let the temperature fall to about 1100 degrees (2012 F), and hold for 3 hours then switch the kiln off. 

If you follow that schedule you should get crystals, maybe as big as an inch and a half in size.
 

*Note that great care must be taken to protect your kiln shelves from run off glaze. Crystalline glazed pots should have glaze catching bowls placed under them. If you don't know what those are, have a look back at my previous 2 posts.

Have Fun!

15 comments:

Peter's Dad said...

Love the pictures, but suggest an earlier night, and soothing book prior to lights out!

Melissa Rohrer said...

Really enjoying looking at these.

Anonymous said...

Turn those feet into napkin rings? Just a thought!

Beautiful glazes!

srgb said...

I'm lost for words Peter, just magnificent and your camera skills too.

Linda Starr said...

scary, careful with that knife, they look like large marbles, wonderful

mikeintonbridge said...

Congratulations - really super results. The first thing I tried when I got my own kiln, with a snazzy electronic controller which allowed me to control the cooling cycle, was crystalline glazing. I used that same blue-and-tan one on a smooth white stoneware. I still have a couple of little bottles. I confess, the trauma of opening the kiln, the grind of making all the extra bits and the grinding if they stuck to the saucers put me off in the end.

Then I resolved to use the glaze on tiles for our kitchen but I found in our new home that the glaze simple wouldn't work for me. Several years later I finally worked out why: the water here is hard and was soft where we lived previously. If I make the glaze with rainwater it works. However my hatred of the cold working required still puts me off returning to it.

Peter said...

Good Morning Dad!
You are quite right of course, but I had a sense of urgency of getting all this down that would have overwhelmed my capacity for sleep, so .... doing the blog was the most "restful" option!! I think Einstein only managed 2 or 3 hours sleep a night and I can quite understand why! :-) "Physics is Fun!" to quote your old Nuffield Physics textbook!

Hi Melissa,
Thank you so much for your ongoing interest and encouragement, it does mean a lot to know that you and others are still following this, even though my blog output has been rather patchy over recent months.

Hello Anonymous,
Feet as napkin rings maybe..., but usually the porcelain rings are fairly battered and splashed with glaze in a way that even dedicated work with the grinder might fail to resolve particularly well. If I really thought about it, there might be something sculptural that could be done by re-firing them as a little stack and letting glaze blobs run and stick them together. I'll give that some thought.

Good Morning Bob,
Lovely to hear from you, with or without words! The camera "skills" would make quite an amusing mini series in itself, as it must be a funny sight to see the potter grimly working with one hand and clutching a camera with the other. Lucky so far that it hasn't ended up in the glaze bucket!

Hi Linda,
The "knife" was a chisel, but it was a challenge finding a camera angle that did not look like I was about to perform painful surgery! Laura assisted with the camera for the photos that worked. I do wear a heavy apron for such tricky work! :-)

Hello Mike,
Good to hear from you, thank you for your interesting comment and encouragement. The hard water/soft water thing is an issue that I have seen crystalline glazers discuss this at times. Potters do report that this does have a profound effect, and some do resort to using distilled water or rain water to solve it.

I can see that hard or soft water could have a significant effect on the behaviour of a glaze when it is sitting in the glaze bucket, (if the PH is wrong glaze ingredients like to form a horrid, unworkable lump at the bottom of the bucket, especially any materials that were slightly water soluble). I am less clear as to how this problem manifests as the glaze is fired as water has evaporated away and only a minor trace of the excess calcium and/or magnesium (which I presume was the cause for it being "hard") from the water would remain and act as a flux, and a very minor one compared to the vast amount of sodium and other "goodies" that are in the glaze materials that the potter has used. But, you and many other potters find that rain water or distilled water makes the difference between success and failure for these glazes, so this does simply illustrate the exciting complexity and wonder of what is happening to a glaze at high temperature when atoms are dancing and electrons jumping!

I agree.... making all those extra bits and all the grinding and so on, is a big downside when working with these glazes. Whilst it does "get to me" a bit at times, I think that the hardest part is trying to come up with a fair retail price for the work. So much effort goes into a lot of the process that the customer just does not see... and then, if a dealer wants to take nearly half of the retail price for selling it... well, the poor old potter ends up with hours of work for almost no return! That said.... I keep on making them!

Sue said...

Peter, excellent work, as always. I love the glazes, the colours and effects. Beautiful.
I hope you and Laura are well and enjoying the spring sunshine and flowers.
Love to you both. ☺

Peter said...

Hi Sue,
Lovely to hear from you on this rather wild and windy afternoon (a strong NW wind has just got up!). We are OK and Spring flowers are very springy! Lots popping up now and Laura darting from flower to flower like a hard working bumble bee!
Love to you both too!

Rhonda said...

Beautiful crystals! Well done!!!! You must be very happy with the results.k?

Peter said...

Hello Rhonda,
Lovely to hear from you. I am very pleased with how the paperweights turned out and..... have been doing a glaze firing of 10 more from around 7 last night to mid afternoon today!!! Hope to unload tomorrow evening or Wednesday morning first thing.

Anna said...

Hi Peter
Such a lot of work but you make it seem worthwhile with such wonderful results.. All the best to you and Laura

Peter said...

Hi Anna,
Nice to hear from you all the way from sunny Australia! We're starting to have a few more visitors through the gallery now that summer is approaching and the garden is flowering away madly. We still remember your enjoyable visit and hope things are going well for you both. Kind Thoughts from us!

angela walford said...

Stunning work Peter! it really is a challenge to get nice crystal growth and you've done a fab job. :D cheers ang

Peter said...

Hi Ang,
Lovely to hear from you. Thanks for the cheery comment, crystals in glazes are certainly not for the faint hearted... The very next firing was a spectacular flop for some reason! Ha..., but they are fantastic when they work!