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Hi,
I am a total newbie to ceramics, but my daughter and I are excited to be starting this new adventure together!    So please bear with me if my topic is showing  such a lack of even the most basic understanding of how things work.

We are planning on creating artistic 'flat' ornaments..   We do plan to 'bisque fire' & then 'glaze fire' our ornaments.     (You'll probably hear from me again when we get to working with our Kiln!)

I have been playing around with creating a few ornaments,  and now have created a couple of plaster molds of my ornaments...   
I poured my slip (premixed & purchased from Dick Blick's) into one of my molds.  But, as the slip dried, there was such shrinkage of the slip, that the center of the item somewhat collapses &  one even cracked, leaving me with a 'bowled ' back of the ornament when what I really want is flat...   

The castings are between 1/4" thick to a very max of 1/2" thick with a maximum diameter of 2"-3".   I have purchased bisque items where they are that thick (with a flat back), so I assumed one can pour slip that thick..  ??

I'd be so grateful for any guidance such as:

1) Suggestions on informative books  or videos to educate myself on the basics of ceramics.  Probably a very good step to move forward!  I have searched YouTube and not found any useful videos dealing with one-piece molds such as what I'm trying to do..  but would so appreciate a highly recommended  'learning the basics of ceramics" book/course/video.
2)  Should I be using a specific type of plaster for my molds - maybe what I used to create my mold is absorbing the moisture too fast?
3)  Should I be using a specific type of slip?   or is Slip even the right material for what we are trying to do??
4)  What might be an expected shrinkage %?     
5)   Do you pour the slip in thin layers before each prior layer is dry?  
6)  Any general suggestions   (other than telling me I might not belong in the ceramic world)?     :-)      

We all started somewhere!

Thank you in advance.

Nancy 

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2 hours ago, NancyJ said:

Hi,
I am a total newbie to ceramics, but my daughter and I are excited to be starting this new adventure together!    So please bear with me if my topic is showing  such a lack of even the most basic understanding of how things work.

We are planning on creating artistic 'flat' ornaments..   We do plan to 'bisque fire' & then 'glaze fire' our ornaments.     (You'll probably hear from me again when we get to working with our Kiln!)

I have been playing around with creating a few ornaments,  and now have created a couple of plaster molds of my ornaments...   
I poured my slip (premixed & purchased from Dick Blick's) into one of my molds.  But, as the slip dried, there was such shrinkage of the slip, that the center of the item somewhat collapses &  one even cracked, leaving me with a 'bowled ' back of the ornament when what I really want is flat...   

The castings are between 1/4" thick to a very max of 1/2" thick with a maximum diameter of 2"-3".   I have purchased bisque items where they are that thick (with a flat back), so I assumed one can pour slip that thick..  ??

I'd be so grateful for any guidance such as:

1) Suggestions on informative books  or videos to educate myself on the basics of ceramics.  Probably a very good step to move forward!  I have searched YouTube and not found any useful videos dealing with one-piece molds such as what I'm trying to do..  but would so appreciate a highly recommended  'learning the basics of ceramics" book/course/video.
2)  Should I be using a specific type of plaster for my molds - maybe what I used to create my mold is absorbing the moisture too fast?
3)  Should I be using a specific type of slip?   or is Slip even the right material for what we are trying to do??
4)  What might be an expected shrinkage %?     
5)   Do you pour the slip in thin layers before each prior layer is dry?  
6)  Any general suggestions   (other than telling me I might not belong in the ceramic world)?     :-)      

We all started somewhere!

Thank you in advance.

Nancy 

Welcome, Nancy!

 

First, I question why you are slip casting. If you are making simple shapes, a slab of clay and then cutting out pieces from the clay with cookie cutters or a needle tool would work well. Slip casting is usually used for more intricate ornaments or pottery. You may be better off using a cone 6 porcelain and rolling that into slabs.

However, slip casting is fairly easy to do, you don't need much practice to make a decent looking piece.

 

Look at these books: https://www.amazon.com/Essential-Guide-Making-Casting-Ceramics/dp/1600590772/ref=sr_1_2?dchild=1&keywords=slip+casting&qid=1585873183&sr=8-2

https://www.amazon.com/Beginners-Guide-Pottery-Ceramics-Everything/dp/178221559X/ref=sr_1_2?dchild=1&keywords=beginners+guide+to+pottery&qid=1585873218&sr=8-2

 

For plaster molds use Pottery Plaster 1 or hydro stone

 

I would use regular firm clay

(for slip) any casting slip, usually a good porcelain one.

 

Shrinkage rate should be on the bottle of the slip. Somewhere around 12-15% probably.

 

Pour all at once, keep refilling. Usually 15 min in a mold is sufficient time for the clay to harden.

 

I think, for right now, slip casting is an unnecessary step (just based on what you have described.) I would start by using normal boxed clay, learn some glazes and how to use your kiln, then move to slip casting.

 

Brandon

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nancy, welcome to the forum.  you will find that the field of ceramics is so large that it is amazing that anyone can learn enough even after a lifetime.  it is a skill that develops over time so be patient with yourself, do not call a learning experience failure.    the product may not be what you wanted but you did learn something by making it.

as you were advised by brandon, and liam there is an easier way to make flat ornaments.   just a few questions here to clarify things.

did you purchase the molds or make them?  if you made them, what kind of plaster did you use?  if you made them, what artistic touches did you use?

do you know the firing temperature of the clay you purchased as slip?

you mention having a kiln,   it is the most important item you have since what you make depends on its ability to  produce the final product.   can you tell us exactly what brand, size and whether you have any "furniture" for it.  that is, shelves, posts to hold shelves up and any other items that you purchased with the kiln.   you must have noticed that a potter's vocabulary is a little different, it is also confusing to new people.  ask any time something is unclear.  there will be a metal plate attached to the kiln with electrical information.   it will not say "sitter", look again.

it will help to send photos of anything you wonder about.   the more info you give, the better answer you will get.   there are many people on this forum and a vast amount of knowledge of all kinds.   do not be hesitant to use this opportunity to learn.

 

 

 

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Excellent advice above.

As for your moulds, are they one piece or multi?

They need to be multi to get a flat back and a detailed front.  But then they need a pour/drain hole.

We really need more details and photos to help you further.  To make your photos small enough to be accepted here, try e-mailing them to yourself and choose a small file size.

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Thank you for welcoming me!   I can already tell I will learn so much from reading other posts & responses.  I am so glad to have found this community!
And, thank you to those that so quickly responded to my post.  I so appreciate  each of  you taking the time to provide some wonderful feedback!

"Brandon" -  I am starting to read reviews now on each book you recommended...     And thank you for the 'to-the-point' answers to each of my questions.
"Liambesaw" - Thank you too for your input!   These are open molds -  I really hadn't considered using them as 'press molds' with clay...    I had thought the smooth silky slip would keep the detail of an ornament with designs more than pressing clay..  And, if we created anything worthy of selling, pouring slip seemed to be more efficient than pressing the clay one at a time.   But, I actually like your idea on starting out simpler and learn the basics as you mentioned - glazes & kiln firing!   So I'm thinking of starting there - but still very interested in using slip in the future!
"OldLady" -   (first, Love your Profile page - with a name of Harper's Ferry -  it sounds like such a great place to live! and enjoyed reading your "Interests" !)    Thank you for the welcome and  your words of encouragement!    So much appreciated!!  Will try to answer your questions... 
1) Since right now I am just getting my feet wet, I made the molds using a product called "perfect plaster" from a big chain Craft store..   likely should change to recommendations by Brandon..
2) The Slip I purchased is Amaco / Cones 05-04  - 15-S Casting Slip by American Art Clay Co..  There is no mention of Shrinkage % on the label. .   Bisque fire to Cone 04..
3) The Kiln is an Evenheat RampMaster II - 810.   This is a very small kiln (inside is 11.25" diameter x 9" deep)  we decided to purchase to start with - for a couple of reasons...   My home is where the kiln will reside and it would be very costly  to add 220v to my existing service panel.. so until we have some experience under our belts, and feel we can progress to the next level, we are okay with the small kiln (using 120v) and do lots of firing!   The furniture we plan to use are 'ornament hangers' but there are several shelves and an assortment of stilts also.   Another reason for this Kiln was it has a controller  making it 'programmable' and somewhat 'automated'.  We thought this could certainly be an advantage for us newbies!  Unfortunately, due to the Coronavirus outbreak, this Kiln we ordered mid-February still has not arrived.. and could easily be May/June or ? before we see it...    But we have plenty to learn while awaiting it's arrival!
4) As far as what we are designing?  We are just starting on designing our ornaments..  Interested in creating a variety of uniquely shaped designs with some level of detail but not too intricate...   equally interested in the Glaze process as we want the finished item to have a very nice - imperfection free - finish (if that is
5)  No pictures yet - nothing worthy of posting...   as we are so at the very beginning of this adventure - which I'm sure you can tell from my posts!
"Chilly" - Thanks for chiming in on suggestions..     Yes, my molds (all 2 of them I created)..  are one piece, open molds for flat ornaments..    so no way really to have a drain hole.. which I think has been my confusion on how to make these flat ornaments with slip from the start - as they do not follow the standard mold process of draining excess slip after set-up time..   I had thought if I poured the slip into my open mold, with a little shaking/tapping, the slip would self level and I'd have a smooth back (except instead I have considerable shrinkage!)    Thanks too for the information on how to post photos.  Good to know!  When ready to 'share' some photos, will use your process.

If anyone has ever have good results using slip in an open mold for a flat ornament/item would love to hear from you...     It sounds like that just may not be the best route!?

Based upon your comments, we think we might try two approaches - and compare the results based upon quality & time consumption: 
1) to use the molds as 'press molds'  using a quality clay..  (once I pick out & purchase a quality clay)..
2) purchase one of the plasters suggested, and purchase a porcelain slip  -  remake mold and  use new slip - just to see if I have a different outcome - primarily less shrinkage - as the rest looked great!.   

Again, I so appreciate your information.
Thank you, Thank You, Thank You!
NancyJ

  

 

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I am curious as to what you mean by ornaments.  Are these something you would hang on a wall, keep on a table or are they for  a Xmas tree?  If the latter, keep them as thin as possible.  1/2" clay tree ornaments are really heavy.  Good luck with your explorations.  L

Edited by LinR
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Hi LinR,

The flat ornament would primarily be intended as a tree ornament since we are trying to keep the size relatively small.  But suppose it could be placed anywhere since we are not focused only on Xmas..   Hoping I can keep the thickness well below 1/2"..   as I agree that at 1/2" thick, the ornament would weigh pretty heavy on a branch.      Thanks for the good luck wishes !!

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nancy, good to hear from you again, sometimes people just disappear if they think they are being told they are doing something wrong.   never  wrong,  just uninformed.   willing to learn?   we love people like that.   you have not mentioned your daughter's age.  chilly works in the UK with children and lots of members do also.   if you can add a location to your avatar, we won't send you out to buy something in a different country.  ( well, maybe not.)

your kiln will dictate the final cone temperature of the clay you buy.   if you are interested in porcelain for some reason, be careful to get something that can be fired (another new word) at that very low temperature.   the cone number is of primary importance, make sure the kiln can easily reach the cone of the clay and not be straining to reach it.   be sure to buy a clay that will mature at the kilns cone.    i have never used a kiln that can be used on household current.    if neil chimes in, he is one of the kiln experts and his advice is golden.

the plaster you used is probably labeled somewhere as plaster of paris.   it is simply not as strong as pottery plaster.   your molds just might not last as long but they will do for now.   if and when you are ready to buy plaster, that is another learning experience.   it comes in 50 pound bags and can deteriorate if not kept totally sealed in a plastic bucket with tight lid.

you might find doll porcelain slip somewhere, it should be a low firing slip.  it may be available in other places than ceramic supply houses.

the design question leads to a discussion of how you could unknowingly make a pattern that has an undercut.   more vocabulary.  avoid undercuts or you might not be able to get the piece out of the mold at all.   btw there is a very useful glossary somewhere on this forum.  check headings.

pictures posted here on the forums are the easiest to see.   some people have their pictures on some outside storage place that can be difficult to access.

topping up your slip as it begins to dry might be easier if you pour a cup or so into a  small long spouted pitcher.    if that cup or so begins to dry in the pitcher, cover it to keep it liquid.  once it gets a skin on it, you must mix it up perfectly into the original or discard it.

just one more thing, stilts are not posts.  posts hold up shelves that may have lots of pots on them.   3 posts per shelf  are usually best.   stilts are a way to raise an individual piece above the shelf so glaze will not run down onto the shelf and stick the piece permanently to the shelf.

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If the slip is shrinking that much you're leaving it on too long.  When you use casting slip you need to pour slip into your mold, wait 10-20 minutes then dump it out.  Then you only leave the clay in there long enough to harden to the point you can remove it.

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@NancyJ, here's the simple answer: your molds and slip are fine, now try this-

Pour in the slip into the mold(s) to the rim, then keep topping it off (without overfilling if possible) until the clay stops shrinking down. This may take several top-offs but don't stop until it shows a slight humping of the center and the sides are pulling away from the edges a bit.

Your plaster is very thirsty and will keep drinking in the water till it's slaked enough. Then, as you know, the piece dries pretty quickly.

The backs should have a rolled looking rim and a slightly indented center when stiff. You can trim off any slops and knurdles when it dries enough to tip out. (When it's too stiff to hold a gentle fingerprint)

Remove from molds asap so the plaster can dry enough for the next casting. You can use a hair dryer to dry the molds, but don't use it on the ornaments.

Pressing 3/8" clay slabs from the bag into your flat molds is another way to work. The molds don't get as wet, but there's usually more trimming needed on each piece 

Edited by Rae Reich
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Slip Casting only tends to be faster and more productive on an industrial scale.

A thousand of the same molds.

Large vats to reprocess slip, since the poured remainder is no longer the same as when it entered.

So my question to you, is..

Do you want to spend the time it takes to create one thousand molds?

You need them to produce a thousand ornaments in one day.

Where, if you are press molding, with which I'm certain with care, you can achieve the same detail, you can make a thousand  ornaments in a day with only a few molds. A reasonable amount of molds to keep in a home studio IMO.

I guess it then depends on how many styles or molds you want to have?

If you will glaze differently 1 design only, slipcast. Have the thousand molds.

If your work will feature different pieces, new pieces, changing shapes sizes etc, you simply won't have space for all the molds necessary to produce a decent amount of work, so I would press mold.

What's most important IMO....

The difference between what happens when you drop a bucket of slip and a bag of clay!

Press molding will allow you much less cleaning time, even if you don't drop a Bucket!

I think you may end up utilizing both techniques, as you define your body of work.

But don't fall for the seeming romance of one over the other.

A successful pottery is a balance between deep romance and cheap thrills!

 

Sorce

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