What is casting slip?

An Etsy customer recently asked what “slip” is (because it is listed under my material section for most of my items) and then, a day or so later, my husband asked what slip casting is, even though he see’s me pouring slip all the time – I suppose he just didn’t know the name that is attached to the process .  It’s another occasion where, because I know what something is, I assume others do too.  So, I though I’d explain this mystery substance that is the basis for most of my products.

Slip is a liquid clay and can be any type of clay from earthenware to porcelain clay.  Water is added to help achieve a liquid state but there is not as much water in slip as you would think.  Actually, slip contains only a little more water than clay that you would use on a wheel or use for slab building.  The magic ingredient that makes clay castable is deflocculant, solutions that contain sodium ions (+) that act to keep the clay particles from packing together and settling.  Of course there are other things that go into making a workable slip, ratios of different raw materials, etc.  But that’s the gist of it – clay, water, deflocculant.  It seems pretty straight forward until, like me, you add too much deflocculant and end up with slip that performs horribly, either gums up or gets so liquid it settles out.  So, on my creative quest, I had to call on my science background and start measuring things like specific gravity and viscosity.  After leaving college chemistry classes, I never thought I’d use a triple beam scale again, let alone own one.  But I do and I use it every week to measure the weight of slip and divide it by the weight of an equal amount of water to determine the slip’s specific gravity.  I’m shooting for a range of 1.74 – 1.76.  Then I take my stoppered Erlenmyer flask and time the amount how long takes for 500 ml of slip to flow out.  It’s all very scientific and important, hee hee.  But really, all this measuring has helped me get a handle on mixing and working with slip.  Thankfully, there is wonderful information in books and online which has helped immensely.  These are a couple of my favorite books The Essential Guide to Mold Making & Slip Casting (A Lark Ceramics Book) by Andrew Martin and Slipcasting (Ceramics Handbooks) by Sasha Wardell.  These deal mostly with porcelain and not stoneware, which is what I use.  Thankfully, Jaun from Laguna Clay has been helpful along the way.

Each day I pour slip, I mix it up well (because it thickens as it sits) and then fill up my molds.  Water from the slip travels through the plaster molds via capillary action, leaving behind a coating of slip on the inside of the mold.  This coating, the cast, gets thicker the longer the slip sits in the mold.  The amount of time that slip is left in the molds varies depending on what it is – a small dipping dish takes about 30 minutes and a stein mug about 60 minutes to get to the right thickness.  When the cast reaches the proper thickness, the slip is dumped out of mold.  The coating of slip that remains inside the mold is allowed to dry until the piece can be handled – this us usually a few hours.

casts of mugs in molds
Casts in molds waiting to be removed.

Then the mold is taken apart and the cast removed.

Stein mug and handle in ceramic mold
Stein mug and handle in ceramic mold

At this point the spare clay from the mold opening is trimmed, attachments (like mug handles) are added

Removing slip cast stein mug from mold
Removing stein mug from mold
Adding handle to mug
Adding handle to stein mug

and and the seam lines (ridges of clay where two mold pieces come together) are removed.  The piece is then let to dry a little more and final trimming is done.  Once the piece is bone dry, it is further sponged to remove any residual traces of seam or other blemishes and to smooth out edges and remove any dust.

Greenware stein mugs
Greenware stein mugs

It is then ready for firing, decorating, glazing……

Golden Retriever Stein Mug
Golden Retriever Stein Mug

I love the process – I was attracted to it immediately.  I thought it would be simple but turned out to be more challenging as I got more into it.  But I’ve meat every challenge with enthusiasm to learn more and am thankful for my achievements.  I look forward to continued learning on the subject of slip.  ‘Cause, just when you think you’ve got something down, the Universe throws a curve – just so things don’t get boring.


Until I Met You

I love this. It just speaks to me. The beautiful girl with the sweet yellow bird on her hand. My own beautiful 9 year old has a really nice little parakeet that looks at her with the same trust as the bird in this image. Priceless.

LubA Arts

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Revamping website

I have spent the last month and a half working in my studio, slip casting, decorating, etc…the usual.  But have also been working on neglected projects like revamping my website, refocusing my energy on my major goals.

My website has been in “maintenance” mode for a month.  I am removing all outdated photos of items that are no longer decorated in that particular way.  The changes will be very drastic.  I plan to cut back to just one item – my Stein Mugs, offered with several different dog breeds.  When I have 20 or so different breeds on my mugs, I will add other items back into my offerings.  This is all a part of me focusing on my goals.  Before, my website had too many items listed but there were not pictures associated with all items – it was confusing and less professional than I wanted.  This way, I can get each item right before adding the next.  It’s the way I should have done it in the first place.  Live and learn, and then keep learning.

Faery Tails Corgi Rescue – Corgi Jubilee


The Corgi Jubilee is an apt name for this wonderful event, considering the Queen’s Diamond Jubilee is occurring as I write, and she a staunch Corgi lover herself.  The Queen’s love of Corgis and the attention that the breed has received lately is both good and bad.  Hopefully the attention will be focused on those Corgi’s in the US that need homes, though likely it will also result in more breeding of Corgis and more dogs needing homes.  That is why the work done by dog rescue organizations, like Faery Tails Corgi Rescue, need support.  You can support this organization by participating in The Corgi Jubilee that is taking place at AKC Museum of the Dog, 1721 South Mason Road, Saint Louis, MO, Saturday June 9, 2012.  You can also donate to them by visiting their website.

Join the folks of Faery Tails Corgi Rescue for their annual fundraiser – a fun filled day of corgis, shopping, silly contests, silent auction bidding, purchasing raffle tickets and enjoying lunch with good Corgis and friends.   All well behaved and leashed corgis and corgi mixes are welcomed. Other well behaved and leashed pooches are welcome to attend too. If you would like to bring something for the lunch table or an auction item, please contact us.  All money raised will go to the care of wonderful dogs who need a fresh start for a wonderful new life.  Help support this worthwhile event.

For more information, please call 314-631-2577 or email information@corgirescuestlouis.org.