L3954F Cone 6 Engobe for Plainsman M340, M390, Coffee Clay

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Make flawless cone 6 ware with clean functional surfaces, even on red burning bodies, using this engobe and this firing schedule.


Cone 6 White Engobe Recipe

Drying and firing shrinkage fitted to Pliansman M390, M340

Code #

L3954B

Batch #

3

Materials Amt
Nepheline Syenite 18.000
Silica 15.000
Ball Clay 54.000
Zircopax 10.000
Bentonite 3.000

Total:100.00

Notes

*This recipe has been tuned to have about the same fired shrinkage as Plainsman M390, Coffee Clay and M340 at cone 6 (we measure this at 6.7% dry-to-fired shrinkage using the SHAB test). We also confirmed fired-shrinkage-match using the EBCT test). If the body you use has between 6.5 and 7.0 fired shrinkage, this should work. Do not ignore this detail. If you apply this as an engobe (e.g. by dipping leather-hard functional pieces), and it is not firing-shrinkage-compatible with the body, it will eventually flake off during use.

Engobes are not slips (normally applied by brushing). Engobes used in pottery are applied thickly (usually by dipping or pouring). It is vital the slurry has the right rheology to work properly. Follow the links on this page and read carefully, it will mean the difference between success and failure.

Ball Clay: We use Old Hickory M23, but you can substitute others (e.g. OM#4, Gleason).

The color is whiter than previous trials (because of the zircopax), but some might prefer a little blue stain to brighten the color. We used 0.2% Mason 6336 with good success, other stains we tried agglomerated and caused specking). A black version, L3954F, can be made by substituting the Zircopax for Mason 6600 stain (7.5-15%). This produces a very high quality black color (e.g. buff-burning M340 with a black stain produces far better color than Coffee Clay).

This is an engobe, it must be applied at stiff leather-hard stage (if you apply it to dry or bisque it will flake off). The bentonite is present to make it sticky and gel better. Many engobes have more bentonite than this, so it can tolerate more (e.g. 5%). But the more you use the slower it will dry.

On application it will rewet leather-hard pieces and they will require significant time to re-stiffen to the same state. Even coverage can normally only be achieved by preparing a slurry of the correct rheological properties and dipping or pouring. It is vital that you have a good mixer and can effectively measure specific gravity. To mix this use the process described on the “Engobe” glossary page at the Digitalfire Reference Library (the "engobe" links on this page go there).

Examples of mixes we have done:
Add the Darvan to the water then add the clay, mixing while doing so.
5000g powder to 3900ml water to 20g Darvan produced less than two gallons having a specific gravity of 1.55 (proportions are thus 100:78:0.4). But after a day it was too fluid and a tiny amount of epsom salts was added to bring it back to a creamy texture. In future mixes we will start with 15 Darvan.

Comments

2020-10-19


Brush-on version: 75g Laguna gum solution, 280g water, 500g powder (makes 1 pint). A good mixer is needed to mix in the last of the powder (or an overnight sit will break up the lumps). This produces a consistency that is very brushable.

URLs

Glaze thixotropy

PlainsmanClays mix..nstructions L3954B

L3954B pictures an..italfire Reference

Information about .. Reference Library

Pictures

L3954B Very sensitive to over deflocculation

Only 3 drops of darvan in 3/4 gallons of slip fixed the problem on the left. The slurry was over flocculated using Epsom Salts.

M390:3954B engobe BiClay strips after drying

These were laminated in plastic form. Two were dried red body side up, two with the engobe side up. Results are very flat, very good drying shrinkage fit.

L3954B engobe:red stoneware biclay cones

The white engobe was prepared in plastic form and rolled and laminated with the red body. The thin strips were dried and fired to cone 6 to find incompatibilities in drying and firing shrinkage. Results are very good, slight curling toward M390 (the Plainsman red burning body) on drying, a little more toward the white slip on firing.

10% black and red stains in L3954B Engobe

Black is Mason 6666. Although color is good, Mason 6600 is the recommend one for bodies. Red is Mason 6021. Much more will be required to get good color.

L3954B with Burnt Umber and Black Stain

Both replace the 10% zircopax with a black pigment. They darken the engobe to near black. But the stain version (Mason 6600) on the right fires blacker and develops the color of this rutile glaze (Alberta Slip rutile blue) much better. It also produces a perfect glass surface whereas the Umber version on the left develops some pinholing in the inside glaze (GA6A Alberta Slip base).

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 92.89 86.63 40.38 41.3 6.0 7.1% 6.7% 2.3%

EBCT - Engobe Body Compatibility Test

MATA MATB BNDR BNFR BCON
1 M390 L3954B 1.5mm/A 3.0mm/B 6.0

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 6 White Engobe Recipe" keywords="Drying and firing shrinkage fitted to Pliansman M390, M340" id="113405" key="LjturwTX" date="2021-02-01" codenum="L3954B"> <recipelines> <recipeline material="Nepheline Syenite" amount="18.000" tolerance=""/> <recipeline material="Silica" amount="15.000" tolerance=""/> <recipeline material="Ball Clay" amount="54.000" tolerance=""/> <recipeline material="Zircopax" amount="10.000" tolerance=""/> <recipeline material="Bentonite" amount="3.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2016-12-12, Modified: 2021-02-01 15:58:21

Black Cone 6 Stained Engobe Recipe

Code #

L3954F

Batch #

3

Materials Amt
Nepheline Syenite 18.000 17.14%
Silica 15.000 14.29%
M23 Ball Clay 54.000 51.43%
Bentonite 3.000 2.86%
Mason 6600 Stain 15.000 14.29%

Total:105.00

Notes

*Fires jet-black, much blacker than any black burning clay body on the market. Because particulate stain particles supply the color this is not messy to work with, just water will completely clean any surface (unlike black bodies made using raw or burnt umber). This will remove from clean plaster batt without leaving any stain.

Comments

2018-04-04

In March of 2018 Joe made up a 500 gram batch of this engobe to make a "gum based brush on version". Used the quantities listed above and added:
75 grams Laguna gum solution
280 grams water.

Last of material added to water/gum mix was a little difficult to stir in. Used a 1 pint jar and tablespoon. Final mix was lumpy, had to let sit overnight and next morning it was much more fluid and lumps had almost disappeared. This must be taken into account if you do not have a high speed mixer.

URLs

Make a brushing version

Pictures

10% 6666 stain in engobe under a clear glaze

Cone 6. M370.

10% 6600 stain bowl

Lots of bubbles. But clay is very black.

L3954B with Burnt Umber and Black Stain

Both replace the 10% zircopax with a black pigment. They darken the engobe to near black. But the stain version (Mason 6600) on the right fires blacker and develops the color of this rutile glaze (Alberta Slip rutile blue) much better. It also produces a perfect glass surface whereas the Umber version on the left develops some pinholing in the inside glaze (GA6A Alberta Slip base).

Black stain L3954F vs. Raw Umber black clay

L3954F black egobe with 7.5% stain

The center bar has 7.5% Mason 6600. The bottom one has 15%. The top one is a body havig 10% raw umber.

L3954F black cone 6 engobe fired bars

M340 mugs with L3954F black engobe, Ravenscrag blue

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
5 92.96 86.72 39.66 39.69 6.8 7.0% 6.7% 0.1%
6 92.99 86.08 40.74 40.75 6.2 7.0% 7.4% 0.0%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Black Cone 6 Stained Engobe Recipe" id="115180" key="m92wck59" date="2021-02-01" codenum="L3954F"> <recipelines> <recipeline material="Nepheline Syenite" amount="18.000" tolerance=""/> <recipeline material="Silica" amount="15.000" tolerance=""/> <recipeline material="M23 Ball Clay" amount="54.000" tolerance=""/> <recipeline material="Bentonite" amount="3.000" tolerance=""/> <recipeline material="Mason 6600 Stain" amount="15.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2016-12-12, Modified: 2021-02-01 16:04:41

Firing Schedule Name

Plainsman Cone 6ox drop-hold-slow-cool

Cone-Art 2818D, exhaust fan on at start of firing

Degrees (Fahrenheit or Celcius)

F

Schedule Type

Rate

Start Time and Temperature

8:00 am at 70F

Program

Step Degrees/Hr Temperature
Monitor
Hold
Time
Accumulated
hrs:min
Time Note
1 300 250 60 1:36 9:36 am
2 350 2100 6:53 2:53 pm
3 108 2200 10 7:58 3:58 pm
4 900 2100 30 8:34 4:34 pm
5 150 1400 13:14 9:14 pm 2195 in large kiln

Notes

C6DHSC
Plainsman kiln cone 6: 2188 Jan 2016 as verified by cones.

Use for defect free glazes that need to crystallize during cooling (e.g. rutile blues). And to get defect free glaze surfaces in others.

If the kiln is full, lengthen the first step hold time to drive out all residual or remaining water from body and glaze (depending on the ventilation in your kiln). This schedule assumes that a good bisque has been done.

If cone 6 still does not completely fall (e.g. you fire heavy loads), increase the hold time in Step 3 by 5 minute increments.