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The MSDS for various glass etching creams all show that they're primarily composed of 4 substances (the composition percentages vary):

  • Ammonium Bifluoride - 20 - 40%
  • Sodium Bifluoride - 5 - 10%
  • Sulphuric Acid - 1 - 5%
  • Barium Sulfate - 1 - 5%

The purpose of the fluoride ingredients is obvious. They decompose into hydrofluoric acid (presumably when reacting with water in the air) and do the actual etching. But why is there Sulphuric Acid? It doesn't react with glass at all.

My speculation would be that perhaps it's a strong desiccant and it serves to slow the reaction?

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    $\begingroup$ $\ce{HF2- + H+ <=> 2 HF}$, resp. $\ce{F- + H+ <=> HF}$ $\endgroup$
    – Poutnik
    Commented Dec 7, 2022 at 20:23
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    $\begingroup$ Using bifluorides with a mineral acid is technically the second best after using directly HF(aq), as nobody wants to manipulate with stock HF(aq) unless absolutely necessary. (One bigger splash can kill you after few hours or days, unless treated. It is extremely painful and may left permanent damage.) $\endgroup$
    – Poutnik
    Commented Dec 7, 2022 at 20:56

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