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Hello,

 

I am fairly new to slip casting (about 9 months), and have been trying to learn as much possible through books and videos. I haven't delved into making my own slip yet, instead I have been using Dover Slip from Miller (Laguna). It is a Cone 6 White Stoneware.

 

I am having some issues with the slip:

 

1) A film forms on top the slip after sitting in the mold for about 10 minutes.

2) When I do the hand dip test no webbing is forming at all. 

3) I believe the Specific Gravity is 1.8 (which should be right) I measured out 100ml and it weighs 180 grams.

4) It is pretty thick, pours out of the mold poorly leaving behind some gunk on the rim of the mold (makes for an uneven lip of my tableware)

5) It doesn't pull from the mold well, sometimes even 2 hours later I still can't get a simple cup out.

 

Just for some addition information the room I am casting in lately has been around 85-95 degrees F, with pretty high humidity. 

 

What I am trying to figure out is if I need to add more deflocculant or if the slip has come over deflocculated from the factory, or perhaps I need to add more water.

 

Thanks for the input.

 

-Matt

 

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neilestrick    1,381

From the mold side of it- are your molds good and dry? With high humidity they probably aren't drying completely overnight. I'd run a de-humidifier in the room. I'll leave the slip side to someone else.

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JohnnyK    87

Re: what Niel said...can you set the molds outside to dry or maybe cook them in your kiln at low temp to dry them out?

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When I first made them ( they are pretty new, only have cast in them about 8 times) I had them set out in the sun all day, then had a fan blowing on them while they sat in the shop for 3 days straight, it's been a couple of weeks since doing that. It could be possible that the humidity is so high, they aren't fulling drying out I suppose. I had a fan on them last night when I left, I will see if the perform better tonight.

 

Also, I talked to Laguna, they are going to check the batch number. In the mean time they told me to add a small amount of Darvan. It did seem to make the viscosity go down a bit, so I will try and see if I can get a successful cast tonight. 

 

-Matt

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Chilly    330

Humidity is your problem.  

 

In the summer my casting takes 10-15 minutes before pouring out and 4-12 hours before removing from the mould.

 

In the winter the times can double or treble.

 

A fan will help, but can be unpredictable.

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neilestrick    1,381

Plaster can stay moist for a long time in humid environments. You really need to get them completely dry before using, and that can take a lot longer than 3 days, especially in a humid environment. Once they're completely dry, they will dry out faster between castings. A fan will help to some degree, but a dry environment is what they really need, which is why a dehumidifier will really help. Another good cheap method is to take a big box and hang a 100 watt light bulb in it to provide a small amount of heat (too much will degrade the plaster, so never put it in on oven or kiln), and make a hole for a small fan to blow in it.

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neilestrick    1,381

Humidity is your problem.  

 

In the summer my casting takes 10-15 minutes before pouring out and 4-12 hours before removing from the mould.

 

In the winter the times can double or treble.

 

A fan will help, but can be unpredictable.

 

For us, the air is much drier in the winter. :)

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Thanks for the tips.

 

I got a dehumidifier to see if that will help. It has been so hot I haven't been working in the studio anyways. I am sure things will operate a lot smoother come this fall. Perhaps I will spend some time making more molds while I wait for better casting conditions.

 

-Matt

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