Cosmic Oilspot
PC-66
Cosmic Oilspot is a satin brush-on glaze from Amaco's Potter's Choice line, fired cone 5 to cone 6. Dark, cosmic, streaked.
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Friendly studio tip for this glaze
Use it on something tall. The flecks pull into streams as they move down a vertical wall, and on a flat dish they just sit there.
The quick version of Cosmic Oilspot
What this glaze does
A dark glaze carrying shimmering flecks that pull into streams and patches as they move. Amaco compares it to a hare's fur glaze, one of the old Chinese temmoku effects where iron separates during cooling and draws fine streaks down the pot.
On a vertical surface the flecks tend to line up and travel. On a flat one they scatter.
How much it varies
The dark ground is consistent. Where the flecks gather depends on the form and the thickness.
Clays that suit Cosmic Oilspot
Opaque and dark. The clay body has almost no influence on the finished surface, which is typical of the darker glazes in this line.
Thirty three of these forty six glazes are opaque, so on most of them the clay underneath is a surface to sit on rather than part of the finished color. The other thirteen see through to some degree, and those are the ones where your clay choice really shows.
Applying this glaze to your work
Three coats, not thinned. The flecks need enough glaze to gather into streams rather than sitting as isolated dots.
How much it moves
Standard clearance at the foot. The visual streaming is not the same thing as the glaze running off the pot.
Amaco's instruction for the line is three brush coats, not thinned, each one dry before the next. Their own guidance says most disappointing results come from glaze applied on the light side. Amaco publishes an application guide showing what too thin and too thick actually look like.
Layering
It is a complete surface on its own. If you layer it, keep the partner simple, since a busy top coat cancels the streaming.
Amaco's own combination tiles usually show two coats of each glaze, which lands four coats total anywhere the two overlap. Their standing advice is to test a tile before committing a piece, and to re-test when a new batch number arrives, since raw materials shift between production runs. Dipping versions of these glazes behave differently from the brushing jars and are much harder to layer.
From The Clay Hole University
More info about Cosmic Oilspot below, but first... Everything we teach about glazing, written down and taught properly. These are the glaze lessons, and they are a small corner of a library that runs from centering your first pot to selling your work.
GuideGlaze Brushing Techniques, Coat by Coat
GuideGlazing Big and Intricate Pottery Faster
GuideGetting the Most Out of the Mega Glaze Tool
GuideMaking, Logging and Dialing in Test Tiles
GuideGlaze Problems, Causes and Fixes
GuideGlazing on the Wheel for Even Coats and Clean Bands
GuideBubble Glaze with Dish Soap
GuideMixing Your Own Glazes: What It Actually Involves
GuideMaking a Glaze Catcher
GuideGetting Great Results with Crystalline Glazes
GuideOxide and Carbonate Washes
GuideWhen to Use Celadon Glazes
GuideHow to Use Dipping Glazes
RakuRaku Firing: Techniques, Tips and How It Works
UnderglazeHow to Use Underglaze: Techniques, Rules and Firing
UnderglazeMishima: How to Inlay Slip and Underglaze into Carved Lines
UnderglazeWipe-Away Texture: Underglaze and Oxide Washes on Bisque
Firing Cosmic Oilspot
Amaco rates the line for cone 5 and cone 6, published as 2167F and 2232F on a medium speed firing, over bisque fired to cone 04. Effects of this type develop during cooling, so a normal cooling cycle serves it well.
None of this is yours to manage. We handle everything on the kiln side, and every glaze on our shelves can be fired safely in our studio.
Common problems with Cosmic Oilspot
Why is my surface flat black with no flecks?
Thin application. The effect needs material to work with.
Why did the flecks streak on the side but not the base?
Gravity. The streams form as the glaze moves on vertical surfaces.
What to put it on
Forms and surfaces
Tall forms with vertical walls, where the streaming can run the length of the pot. Bottles and vases show it best.
Colors beside it
A dark field with metallic flecks. It frames warm glazes well and is a strong base under lighter floats.
Food and function
Amaco rates this glaze food safe and dinnerware safe, lead free and AP Non-Toxic.
Every glaze in the line is lead free and, by Amaco's rating, dinnerware safe except PC-4 Palladium and PC-64 Aventurine. Amaco's own label carries the standard caution that anyone producing tableware should test finished ware, because firing temperature and contamination vary between kilns.
Our test tile pots
Every glaze family on our shelves has its own test tile pot, and it is the fastest way to decide what to put on a piece. It is a fired pot wearing the whole family, one numbered tile per glaze, on a surface built to show you what that glaze actually does rather than just what color it is.
- 1Find the pot The brand and family name are written on the rim. This glaze lives on the Amaco Potter's Choice pot.
- 2Find the tile This one is tile #35. The numbers match the ones in the Glaze Bible.
- 3Read it properly Look at what the glaze does across all four textures, not just what color it is.
What to look at on the tile
Some glazes tell you loudly that they run. Others hide it. Look at how the brushed lines fired: crisp edges mean a stable glaze, and edges that went soft and fluid mean it moved, and it will move on your pot too.
Other glazes close to Cosmic Oilspot
Cosmic Tea Dust is the brown, sparklier relative. Temmoku holds the same dark ground in a satin matte. Ironstone gives the dark brown with a bronze float.
Looks great paired with
Put these on the shelf beside it, or on the next pot in the same set.
About the Amaco Potter's Choice Family
Potter's Choice is the line Amaco built so an electric kiln could do what a gas kiln does. Released in 2004, it reaches for the depth of cone 10 reduction glazes at cone 5 and cone 6 in ordinary oxidation. That is the whole premise, and it is why the surfaces break, pool, float and shift instead of sitting flat.
It is one of the most layered brushing lines in American pottery, and Amaco keeps a public library of combination tiles for it. Most of the effects potters chase come from two of these glazes meeting on one pot.
Made by Amaco, a company that has been building glazes and kilns in Indianapolis since 1919. The Potter's Choice line arrived in 2004 and has been a reference point for mid-fire reduction looks since.
More ways to pick a glaze
Membership levels that may use this glaze: None. This glaze is in the studio for Dan's use only. You are welcome to buy your own bottle.
Not sure whether this glaze suits what you are making, or how it works with our system here? Ask an instructor. That is what we are here for, and a two minute conversation at the shelf beats a fired pot you did not want.
About these images and what your pot will actually look like
We have done our best to represent every glaze here accurately, and you should still expect your pot to look different from what is on this screen.
Our glaze tile images are digitally created. They are built to show the character of a glaze, not to be a color match.
A screen is not a printout, a printout is not a test tile, and a test tile is not a finished pot. Each step in that chain shifts what a glaze looks like, sometimes a lot.
On top of that, the pottery itself changes the result: the clay body, how thick the glaze went on, whether it was brushed, dipped or sprayed, what was layered under or over it, where the piece sat in the kiln, how hot that spot ran, how fast it cooled, what was fired next to it, and how much texture the surface had. Two pots glazed from the same jar on the same day can come out different.
Treat every image here as a starting point, and treat a test tile fired on your own clay as the real answer.