Custer Spar
A standard material in Glazecalc's library: its oxide analysis, unity contribution and hazards.
What it is
- Kind
- Feldspars and stones
- Status
- Discontinued 2023
- Formula
- SiO₂ 68.5%, Al₂O₃ 17%, Fe₂O₃ 0.15%, Na₂O 3%, K₂O 10%, CaO 0.3%, LOI 0.3%
- Also called
- Custer, Custer Feldspar 200 mesh, Pacer Custer Feldspar
- Made by
- Pacer Corporation (Pacer Minerals), Custer, South Dakota
- Sold in
- US
- Similar materials
- G-200 EU Feldspar , Mahavir Potash Feldspar , G-200 2R Feldspar , Potash Feldspar (Valentine Clays) , Feldspath potassique ICE 10 (Imerys Spain) , Potash Feldspar K200 (Thailand)
- Source
- Pacer Corp. 'Potash Feldspar Data - Custer Feldspar Technical Data Sheet', revised 3/23/05 (Internet Archive copy of pacerminerals.com, captured 2015-06-03) (2005-03)
For decades the most common US potash feldspar, mined in South Dakota until Pacer shut down in 2023. Use G-200 EU or Mahavir instead; they are lower in iron, but test, because the swap is not always 1:1.
Oxide analysis and unity formula
Glazecalc has the analysis of Custer Spar as weight percent of the raw material. The unity contribution is the moles of each oxide in the amount of Custer Spar that holds 1.0 mole of flux, which is how Glazecalc adds it into a recipe's unity formula.
| Oxide | Weight % | Unity contribution |
|---|---|---|
| SiO₂ | 68.5 | 7.129 |
| Al₂O₃ | 17 | 1.043 |
| Fe₂O₃ | 0.15 | 0.006 |
| Na₂O | 3 | 0.303 |
| K₂O | 10 | 0.664 |
| CaO | 0.3 | 0.033 |
- Equivalent weight
- 625.33
- Fired weight
- 623.45
- Loss on ignition
- 0.3%
The equivalent weight is the grams of Custer Spar that hold 1.0 mole of flux. The fired weight is what is left of that after firing.
Hazards and safety
Hazards: Contains crystalline silica; avoid breathing the dust.
Use it in a recipe
Add Custer Spar to a recipe in the Glazecalc calculator to see what it does to a glaze's unity formula.