Mt Vision Clay

Collection

The clay is collected from decomposed granite found in road cuts or similar excavation points around the property. It's a primary clay meaning it has decomposed where it was originally deposited and has not been weathered from water or wind transport.

Processing

The material is pretty gritty and needs to be sieved to collect the clay particles using a 60M mesh. Here is a picture of the resulting slip.

Once dry enough, a pinch-pot and test bar was formed as shown below. The clay does not pass the coil test, cracking as shown.

The results of drying and bisque firing are provided in the table below. The bisque fired vessels are shown in the cover photo.

Val Cushing's notebook states for an average plastic clay suitable for wheel throwing, Wet to Dry shrinkage of ~6% is normal and another 6% - 8% is expected from Dry to Bisque, or 12% - 14% total.

Levy, Shibata & Shibata in Wild Clay, give an example for somewhat similar looking yellow clay of 4.4% + 6% = 10.4% shrinkage.

We observed 9% + 4% = 13% shrinkage.

Levy, Shibata & Shibata record 16% water in their clay and we observed 27%

Cushing states absorption of ~5% is expected at any temperature while Levy, Shibata & Shibata recored 22% at Cone 04, but < 2% at Cone 10. We measured 16% at Cone 05 and 4% at Cone 6.

We'll retest a few times given this is just one data point.

Levy, Shibata & Shibata also note the following general characteristics for clay bodies:

Throwing clay bodies

• Shrinkage: high
• Water absorption: low
• Texture: fine
• Plasticity: high

Hand-building and slab bodies

• Shrinkage: medium
• Water absorption: medium
• Texture: medium
• Plasticity: medium

Without further modification of the clay, I would classify this clay as

• Shrinkage: high
• Water absorption: Medium at Cone 6?
• Texture: fine
• Plasticity: high

Below presents the final results fired to Cone 6 and glazed with the Mt. Vision Granite base glaze 70% granite / 30% Wollastonite / 10% Silica + 10% Red Iron Oxide.

Remarkably, it fired seemingly perfectly.

Since this initial tests I have thrown the clay and bisque fired it (photos coming). The results were remarkably good. More to come.

Below are results for a repeat of the clay testing process with a test bar that more closely mimics the thickness of a wall of pottery (the prior test bar was, pretty much a bar). This test uses a new batch of clay that results from a more "industrial" batch. So far I've made 25 pounds of clay using a sieving / drying process that I will explain later when I have time.

Test 2