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Member Since 28 Apr 2013
Offline Last Active Today, 09:17 AM

Posts I've Made

In Topic: Air Pen, Anybody Mixing Slips Or Glazes For This?

01 May 2015 - 09:33 AM

Marcia, to state the obvious: if you have any red copper oxide about it might be worth

trying that as well, in case it flows better. I've only used it once, but IIRC it seemed less

clumpy than the carbonate (I had to add a drop of detergent to kill its the wax coating).

In Topic: How To Avoid Thin Porcelain From Breaking?

30 April 2015 - 03:52 PM

Hi Peterh, 

I don't think so, since am not using the glue on the part's which i join together, am just using it on one side and sometimes on both the sides.


Thanks for the info.

In Topic: Green Soap And Drape Molds

29 April 2015 - 02:01 PM

Whats so special about this soap? I use any oil that is to hand.


As I understand the original craft process.

Real soft soap (i.e. the more soluble potassium soap as found in potter's soap) applied in

the old-fashioned multi-coat way reacted with plaster surfaces to form a thin layer of calcium

stearate (calcium from the plaster and stearate from the soap). This was reputedly particularly

effective in preventing fresh plaster adhering to old plaster.


Personally I use a 50:50ish mix of Fairy Liquid and water when casting plaster moulds for slip-casting.

It's ready to hand and works well enough.


Perhaps the old mould makers (with their extensive use of both plaster masters and block moulds) had

larger plaster-to-plaster surfaces to worry about -- or needed to achieve higher standards of finish.

In Topic: Hydrometer - Trying To Get The Hang Of This!

27 April 2015 - 10:21 AM

So in glazing I get information that says glaze should be around 140 to 160 sp gr but the readings are for 1.xxx.


I think that somebody has lost a decimal point from the 140 & 160 figures. [*]

As a point of reference the sg of lead is 11.35, so figures over a hundred are definitely unrealistic.

The 1.xxx figures do sound like sg readings.


Glazes do not have a universally desirable specific gravity range like casting slips. The same glaze can be used effectively by different people and in different processes having quite different specific gravities. We have seen glazes with a specific gravity approaching 1.7, others at less than 1.4. This is not only due to the difference in glaze materials and the way they suspend and interact in the slurry, but it is also common for people to add flocculants and deflocculants to glazes. Here is an example of the instructions for one commercial glaze sold as a powder:


The 0-70 scale sounds like it might be measuring in degrees Baume.

e.g. see https://www.aardvark...cts.php?cat=398

Degrees Twaddle is another relic from the past you sometimes see used, especially for sodium silicate.

Regards, Peter


* Of course if somebody is writing down (or calling out)  lots of figures in the 1.xx range

they may find it easier and less error-prone to leave the decimal point as implied.

In Topic: Luster Crackle

24 April 2015 - 09:57 AM

I'm a little confused, by the wording of your query. Are you after wide (>1mm)

cracks in a resinate luster?


If so, I've always believed that it was done with "painterly" effects. That is

crackle-paint style magic resulting in the luster layer being in its crackled

state before firing.


I believe that there are quite a few painterly tricks-of the-trade (including spraying

drops of meths onto the wet luster) that I'd love to read about.



Added: Not quite what I was thinking of, but see:


... especially click View Larger Image then select the image of 7 vases