Grit Blasting

A strong type of masking tape was cut into the size of a porcelain tile, then using a craft knife a design was cut into it. Once finished, the tape was applied to the tile and wrapped around the edges to strongly secure it in place. Ensuring our face masks were on (as so brilliantly demonstrated by Debra and I), we turned placed the tile into the grit blaster tank and secured the lid. Because there wasn’t a tight seal around the top of the machine, grit was able to get out and circulate into the surrounding area which presented a health hazard to us, therefore the face masks were a necessity. I placed my hands into the provided grit blaster gloves and held my tile from the outside of the box. Pulling the trigger, grit was powerfully thrust into the tile. Areas of the tile unprotected by the masking tape were worn away by the grit. Once the grit blasted was safely turned off at the plug, I was then able to retrieve my tile and remove the masking tape. This revealed the design I had cut into the tape. I didn’t particularly favour this technique as the tape came away very easily and according to the technician the grit blaster wasn’t even that powerful so stronger tape should have been used. I found the depth of the design was completely dependant on how long you left the grit blaster aimed at that particular spot for which created an unpredictable finish. This was difficult to counteract as it was almost impossible to see into the box as the process was occurring. Overall I much preferred the Shellac resistance solution as it was much easier to control.

 

Shellac Resistance

Using Shellac resistance solution, I painted several designs relating to my human form project with a paintbrush onto the greenware porcelain tiles I’d previously made. Where the shellac had been painted, water could not touch which meant that when I applied a wet sponge to the surface and rubbed away at it, the areas which weren’t protected by Shellac turned into porcelain slip and rubbed away leaving a design which protruded out of the tile leaving a textured surface. I liked that it didn’t take long for the Shellac to dry but found that small applied areas of it rubbed away with the sponge which defied it’s whole purpose of being a resistant solution. Overall an interesting method which I would enjoy using again.

 

Porcelain Tiles

Ensuring all surfaces were clean and covered with paper (as due to the white colour of porcelain, dirt is picked up and very visible, I rolled out several slices of ming porcelain clay with a roller and some guides to make sure that the thickness was consistent with each slab. Then using a square cutter I carefully pressed into the clay to cut out a square piece of clay. Removing the excess clay, I picked up the square slab and placed it on a board to dry. Unfortunately I wasn’t aware that porcelain has a strong memory and from when I lifted the slabs up to move boards it remembered how much I bent it so once dried, they were curved and very much not straight. To solve this problem in the future, I will place a board on top the drying slabs to ensure they dry flat.

Porcelain Shrinkage Rates

The shrinkage rates of all clays sold on Valentine Clays (the biggest distributor of clay in the UK and overseas) can all be found on the following PDF file. Please click on the following link to be directed to the PDF stating all this information.

technical-information

Take note of the porcelain shrinkage rate which is at an astonishing 18% when fired at the recommended 1200 degrees in a kiln. This is a factor I must consider seriously when producing my own work as almost 20% of whatever I produce will be lost. To combat this I must test the specific batch of Ming Porcelain I’ll be using to model with and compare it to the suggested 18% shrinkage rate to see where it stands in this spectrum. To do this I will cut a slice of the clay into a ten centimetre square, then measure it throughout the various stages of drying. Once its final firing has been completed, I will use a ruler to see just how much the slab of clay has shrank. With this information I will then know how much bigger to originally model my work to allow shrinkage and end up with the desired size once fired.

 

 

Porcelain Tips

Building onto a form that’s too soft causes slumping. Adding softer clay onto a form that is too dry results in cracking. Altering and/or bending a form that’s too dry or leather hard causes warpage and cracking.

In general, join only pieces of similar dryness and reinforce all joints with extra clay and compress them together with a rib.

Slow and even drying is critical. Periods of rest, where the pieces are wrapped in an airtight chamber to slow drying and redistribute moisture, do help. The clay has a chance to get used to its new form at each phase, without having one part dry too quickly for the rest of the piece.

Another valuable technique is to restrict movement of the piece during the drying phase.

 

All information in this post is a direct copy from the website stated below:

http://ceramicartsdaily.org/ceramic-supplies/pottery-clay/persnickety-porcelain-how-to-minimize-your-loss-rate-with-this-gorgeous-yet-difficult-material/

Facts about porcelain according to ‘Ceramics for Beginners- Why I Use Porcelain Clay for Pottery’

• The more platelets there are in your clay the further you’re going to be able to stretch your clay out.
• If you drop it after a firing you’re less likely to break it.
• Porcelain has a vivid white colour to it before firing and after firing, even with some glazes applied over the top compared to other clays.
• It’s ‘kinda like a bad kid’ as it tends to do what you don’t want it to do whilst throwing it.

 

Overall, it has a prettier finish than most clays but is significantly more difficult to sculpt or throw.

Special Techniques

“Pate sur Pate” Fawn Zeller discovered a technique
called “Pate sur Pate” which
changed the way she sculpted in porcelain forever.
Tiny detail in her small work was often applied with wet slip,
to which white vinegar
had been added to thicken it to a buildup consistency.
Note: Fawn Zeller used very little vinegar to thicken slip
that she was applying to
her sculpt in liquid form. Other artists needing larger pieces
of clay while working in more traditional additive processes
might pour a bit of
slip onto a plate of hard, dry plaster to draw excess water out.
Fawn started sculpting in the customary manner by manipulating
porcelain clay in a moist,
leather hard stage – always keeping it moist throughout
the sculpting process but was
frustrated by the difficulties of keeping her small
sculpts consistently wet.

Porcelain doll maker technique:

Direct sculpting can be started before the greenware is even leather hard!
While doll artists are taught to be EXTRA careful when handling greenware
for larger dolls, miniature doll artists have found that
they can really abuse their greenware and get a startlingly good finished
product! To keep greenware from splitting and cracking in the kiln,
you often have to prop larger pieces and handle the wet greenware
VERY carefully … this isn’t a problem with miniatures (those dolls 7″ and under).

They regularly take miniature hands, cut the fingers apart and reposition
to articulate the hands before the greenware is even leather hard!!!
With a sharp scalpel (be careful), cut apart the fingers …
don’t try to cut all at once, but gently score through.
Then, using a sable brush dipped in distilled water, you can refine
the cut edges and even move the digits to make a pointed finger,
curled hand, fist, or anything that your heart desires. Set aside
the greenware, let dry as usual, clean and fire to bisque!
The same method can also be used to reposition heads! Experiment!

All information on this post is a direct copy from the website found below:

https://kathyoconnellsart.wordpress.com/2011/07/22/porcelain-clay/

Tips for working in Porcelain

Keep it Moist!
Early NIADA artist, Fawn Zeller, started sculpting
in the customary manner by manipulating
porcelain clay in a moist, leather hard stage
– always keeping it moist throughout the sculpting process.
While working in this traditional manner,
she was frustrated because her clay sculpt would
change from day to day due to an uneven drying
even though it was being kept in a damp enclosure.
Daily, she needed to re-wet it,
manipulate it;
or add wet slip to smooth out distortions.
Fawn said, “It would take at least three weeks of
manipulation until the clay itself
finally seemed to give up and the sculptor,
at last, was in charge”.

Molds
If molds are used at all, these castings typically
have minimal detail so most of the
sculpting is done via direct clay manipulation.
The cast clay is promptly removed from the mold
before it is even leather-hard. In
this very wet and extremely fragile state,
they start to sculpt with complete sculpting
freedom yet do not have to worry about
hollowing out later!

Make it hollow
Most clay must be hollow before it is fired
so that all the clay is a consistent
thickness in hopes that it will all vitrify at the
same rate without any distortion. Fawn Zeller hollowed
her pieces in the traditional
manner by cutting them in half,
removed the excess clay in the center,
then carefully rejoined the backs to the fronts.
Marlaine Verhelst starts her sculpts by laying
her clay down over a Styrofoam form which
when removed leaves a hollow consistently
thick sculpt ready to fire. As noted above,
others start off with a set of simple hollow
Castings.

Safety note: Inhaled porcelain dust can be fatal over time.
Protect your lungs when
cleaning, sanding or direct sculpting porcelain!

All information on this post is a direct copy from the following website:

https://kathyoconnellsart.wordpress.com/2011/07/22/porcelain-clay/

Drying phases & Supported Processes

Phase: soft cheese        altering and building (additive)

Processes Supported:

• changing the form’s shape
• adding onto the form
• other additions (handles, knobs)
• texturing surface

Things to Remember:

• slip and score all joinings
• compress joints with a metal rib or wooden tool
• perform any bending of the walls or altering of curves

Phase: hard cheese               trimming and refining (subtractive)

Processes Supported:

• trimming
• rasping away areas of form
• cutting away clay
• carving patterns

Things to Remember:

• basic form should not be altered
• perform subtractive processes to lighten form or add aesthetic elements

Phase: hard cheese         trimming and refining (subtractive)

Processes Supported:

• trimming
• rasping away areas of form
• cutting away clay
• carving patterns

Things to Remember:

• basic form should not be altered
• perform subtractive processes to lighten form or add aesthetic elements

 

Phase: stale cheese            dry shaping (subtractive)

Processes Supported:

• clean surface up
• lighten form further
• soften edges
• trimming or scraping with rib

Things to Remember:

• just before the piece is bone dry, it responds very well to having its surface scraped or trimmed
• if the work has become bone dry, you can sponge it down to do some of these processes

 

Phase: bone dry           erosive action (subtractive)

Processes Supported:

• sponging
• some light carving

Things to Remember:

• sponging the form down reduces sanding, erases unwanted marks, and softens edges
• don’t add too much water!

 

All information in this post is a direct copy from the following website:

https://kathyoconnellsart.wordpress.com/2011/07/22/porcelain-clay/