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Member Since 28 Apr 2013
Offline Last Active Today, 04:00 PM

Posts I've Made

In Topic: Crazing With Commercial Glazes And Bisqueware?

Yesterday, 05:52 PM

Nerd, this may be of interest:


My first impression is that the plate doesn't conform to this pattern, while the stress-test does. 

In Topic: Glaze 101

23 September 2016 - 11:49 AM

For the cat fanciers who haven't already seen them, three pages of kiln felines:


... look at the larger versions.

In Topic: Making Copies Of The Mother Plaster Mold

20 September 2016 - 05:49 AM

Mark, what's a reasonable production rate per mould?


But as I have only one mold of each shape, casting process is slow, I can cast only up to two cups a day from each cup.


In Topic: Making Copies Of The Mother Plaster Mold

19 September 2016 - 04:56 PM

A book I highly recommend as a 2nd book on mould making is:
Chaney [and Skee], Plaster Mold and Model Making.

... if you're quick there is a 2nd-hand copy going for ~17$
https://www.amazon.c...nd Model Making

Besides giving a lot of useful advice on designing/making multi-part moulds, pp62-81 is a worked example of making a 2-part+spare

mould of a frog, then making the associated plaster block&case-moulds. It also has a very interesting section on plaster-build-up as

an alternative to the usual clay-bed method of making multi-part moulds.


Making plaster multi-part block&case moulds looks to be a lot of work!


Another approach I've seen describes uses a flexible casting rubber to make one-piece block-moulds for each part of your master-mould.

Relying in the flexibility of the rubber to release your master-mould parts (after casting the rubber), and your copy-mould parts (after casing

them in plaster). Sounds more expensive, but a lot easier. Not, I hasten to add, that I've any experience with casting rubber. Finding the

right product may be a problem, and I'm unsure what effect it would have on your master-mould parts.

... this sort of thing:


In Topic: Does Magnesium Make Clay Gray? Talc Testing

17 September 2016 - 05:25 AM

... as I was saying.


I cannot think of any obvious yellow pigment that might be involved, although I do feel that

iron might well be involved somewhere.


Looking at the differences between bar 4 and bar 5.

MgO down 1.-7 -> 0.55, Fe stable 0.17 -> 0.16, TiO2 up 0.03 -> 1.06

Which sort of argues for Ti involvement. 

Well TiFe2O5 (pseudobrookite) is certainly yellow enough, as seen in "marbled terra sigillata"


... I would love to hear of any other slip or glaze that uses pseudobrookite as a colourant, and

the conditions under which it can be reliably produced.


It would be nice if the colourant was an Mg compound. Magnesium ferrite (MgFe2O4) is a potential

candidate, but I've usually seen it mentioned as a reddish brown colour:

- as an oil colour


- as an iron-red glaze



Although the colour is described as "presenting a yellow-orange color" here:



Anybody have any thoughts on candidate yellow pigments, and why it only appears in one of the test bars?



Added: This paper suggests that getting pseudobrookite to work as a yellow ceramic pigment isn't that easy,

with a tendency to produce browns.