The passage talking about the substance resulting from a mixture of specific bird droppings with specific plant saps only says that it causes blindness (andhīkaraṇam añjanam):

śārikā-kapota-baka-balākā-leṇḍam arka-akṣi-pīluka-snuhi-kṣīrapiṣṭam andhīkaraṇam añjanam udakadūṣaṇaṃ ca || (AŚ 14,1.15)

“Dung of Myrna bird, pigeon, Baka-heron, Balākā-flamingo, made into a paste with the milk of the plants Arka, Akṣi, Pīluka, and Snuhi, produces a collyrium that causes blindness and poisons water” (Olivelle 2013: 422)

The two translators refer to this andhīkaraṇa añjana with a view to establishing the meaning of yogāñjana in AŚ 4,10.13.

As an interim summary let it be noted that

first, only (4 species of) birds are enumerated in this context. Their droppings have high uric acid levels.

Second, the sap of the two identified plants (of altogether 4 plant species), arka and snuhi, are spoken of as “corrosive” (arka) and “caustic” (snuhi).

This is what the Wikipedia has to say about the spurge: „The milky sap of spurges (called „latex“)“ is said to have „caustic effects“: “In contact with mucous membranes (eyes, nose, mouth), the latex can produce extremely painful inflammation. The sap has also been known to cause mild to extreme Keratouveitis, which affects vision. […] wearing eye protection while working in close contact with Euphorbia is advised. […] severe eye damage including permanent blindness may result from exposure to the sap.”

What effect would a conglomerate of highly acidic bird droppings and caustic plant saps exercise on the unprotected eye? The notion of “poisoning” is less likely than that of causing severe burns. So far everything points therefore to "acid" as the technique of blinding recommended in the AŚ, as spontaneously suggested by Christophe Vielle.

Regards,

WS