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Diz

Member Since 26 Aug 2012
Offline Last Active Today, 09:50 AM
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Topics I've Started

Making Plaster Molds

15 February 2015 - 10:45 PM

Hi All,

I have just finished making over 200# of plaster molds for our local Art Center and have come up with a few questions.  This is not my first time to make , but with the quantity I made, I seemed to have a variety of different ‘problems’.  I actually only ‘lost’ about 5 pieces of 50, so I feel quite successful as I do not work with plaster that often.  With your help, perhaps what I perceived as ‘problems’ will not repeat in future mold attempts.

For my molds I used new pottery plaster.

I weighed out my water and pottery plaster, as directed with my molds, to the ratio of.7 .

Plaster was sprinkled over the water and then left to slake for 2 minutes.  I then mixed gently from the bottom, getting rid of all lumps.  Then I let sit a couple minutes more, gently mixed, and poured it gently into silicone sprayed molds.  (Most of the time the plaster settled/slaked under the water but several times not all of the plaster settled so I had extra mixing – I did not notice any difference in my water temps or time – any ideas why it did not settle – plaster set up quickly).

I learned that water should be cool rather than warm or it sets too quickly.

Several times, altho the plaster was mixed well, as it set in the molds, a thin layer of water formed on top – what did I do wrong?  (I just laid a paper towel on the plaster to soak up the water.)

Also, twice the plaster did not even get warm -  why?  But it set up and appears OK.

I thumped my molds on the floor after filling to get rid of air bubbles but occasionally I had a few, very small, bubbles show up.  They don’t look large enough to cause surface problems in my clay – we’ll see.

I have been told to wait to fill the molds until you can draw a finger across the mixed plaster leaving a slight indentation in the mixed plaster surface – is that right?  At times it then seemed to set very quickly once I started to pour. 

I did learn that different brands of silicone release differently.

Molds have dried nicely by placing them in the area of our wood burner – can do a lot more at a time rather than in an oven!  However they do take about 4 days to dry.

Thanks for your comments!  They are always appreciated!  I learn so much from this forum!!


Oops - I Added Too Much Sodium Silicate To My Slip

28 October 2014 - 04:52 PM

Trying to mix some slip using slop and chunks from a recycling bucket and added too much sodium silicate - is there an easy way to thicken the slip up?  Right now it is like skim milk.

 

This is one of those times when I added more than intended and now I know why I should proceed slowly.


Firing Down

06 October 2014 - 07:04 PM

Temps are cooling here in MN and this Fall and maybe winter, I'd like to continue to fire my gas kiln.  I have an Olympic Torchbearer firing on LP and to Cone 10.  I can control a slow heating up when the kiln is cold in the AM but am wondering how, after reaching temp,  I go about slowing the cooling (and for how long) in a proper way so that glazes do not bubble from rapid cooling and pieces do not crack from shock.  My kiln is in an enclosed shed but the only heat there is from the kiln.  I don't want to damage my kiln or pottery just for a firing or 2 in the winter.  On a usual warm weather firing, I can unload the kiln about 36 hours after firing is completed.

 

I appreciate your sharing of knowledge.


How To Soften (Liquify) Sodium Silicate

06 May 2014 - 07:56 PM

Decided to make some more slip and when I went to use my sodium silicate I found that it has 'set' in my jar, like jelly, but stiffer.  I can poke holes in it but it is not at all 'liquidy'.  Is there a way to breathe life back into it?  Since I do not use it too often might there be a better choice for defloculation that has a longer shelf life?

 

Once again I turn to the Forum Font of Knowledge ....THANKS!

 

Diz


Dvd Vs. Book

18 March 2014 - 06:31 PM

Hi All,

 

I enjoy all the info given in the CAD daily emails and enjoy watching the included video clips but I am 'old-school' and enjoy my books - the feel of the paper in my hands.  As much as I love the info shared in the videos, promoting the DVDs, I cannot bring myself to purchase a DVD (at $40-60) since I would have to use a DVD player each time I needed its info.  I would in a flash purchase many of the books about the same info.  At this point when I see a book to buy, I need to 'check my library' to see if it is a new book to me...and I am not into Kindles either.  Am I a lone dinosaur or are there others out there who feel the same way I do?

 

Diz

 

(Hope this is posted in the proper forum.)