text: One of the zilches has been rediscovered. This is the zilch known as "optical chirality". This name was given by Tang and Cohen since this zilch determines the degree of chiral asymmetry in the rate of excitation of a small chiral molecule by an incident electromagnetic field.
  A further physical insight of optical chirality was offered in 2012; optical chirality is to the curl or time derivative of the electromagnetic field what helicity, spin and related quantities are to the electromagnetic field itself.
  The physical interpretation of all zilches for topologically non-trivial electromagnetic fields was investigated in 2018.
  Since the discovery of the ten zilches in 1964, there is an important open mathematical question concerning their relation with symmetries. (Recently, the full answer to this question seems to have been found ). The question is: 
  What are the symmetries of the standard Maxwell action functional :
   (with , 
  where  is the dynamical field variable) that give rise to the conservation of all zilches using Noether's theorem? Until recently, the answer to this question had been given only for the case of optical chirality by Philbin in 2013.
  This open question was also emphasized by Aghapour, Andersson and Rosquist in 2020,
  while these authors found the symmetries of the duality-symmetric Maxwell action underlying the conservation of all zilches. (Aghapour, Andersson and Rosquist did not find the symmetries of the standard Maxwell action, but they speculated that such symmetries should exist ).
  There are also earlier works studying the conservation of zilch in the context of duality-symmetric electromagnetism, but the variational character of the corresponding symmetries was not established.
  The full answer to the aforementioned question seems to have been given for the first time in 2022, where the symmetries of the standard Maxwell action underlying the conservation of all zilches were found. According to this work, there is a hidden invariance algebra of free Maxwell equations in potential form that is related to the conservation of all zilches.