For the recently reported production (January 2017) of metallic hydrogen in the laboratory - what is the evidence exactly? My google news page has burst forth the news that metallic hydrogen has been produced in a laboratory using a diamond anvil cell. Only one service mentions (at this particular moment) that it has been called into question at - at least - premature. That can be read about in Nature: Physicists doubt bold report of metallic hydrogen
Here I only want to ask about the evidence. Is it only the sudden change in visual appearance change as recorded in a camera on top of the microscope, at a specific temperature and pressure? That it "looks shiny?" Or is there actually more direct data than that?
note: I am not asking if the data is sufficient or not, nor if it is convincing, or metallic or not. Just a narrowly defined question about the extent of the observations that have lead to the proposal that a metallic state was achieved.
 
above: potentially three states of hydrogen as viewed in a diamond anvil cell, from here.
 A: Too long for a comment.
Abstract from https://arxiv.org/abs/1610.01634 

We have studied solid hydrogen under pressure at low temperatures.
  With increasing pressure we observe changes in the sample, going from
  transparent, to black, to a reflective metal, the latter studied at a
  pressure of 495 GPa. We have measured the reflectance as a function of
  wavelength in the visible spectrum finding values as high as 0.90 from
  the metallic hydrogen. We have fit the reflectance using a Drude free
  electron model to determine the plasma frequency of 30.1 eV at T= 5.5
  K, with a corresponding electron carrier density of $6.7\times10^{23}$
  particles/cm$^3$, consistent with theoretical estimates. The properties
  are those of a metal. Solid metallic hydrogen has been produced in the
  laboratory.

Edit: As requested, adding Figure 3 from the paper. 

Fig. 3.  The energy dependence of the normal incidence reflectance off of 
SMH and the rhenium gasket (P=495 GPa) at liquid nitrogen and liquid helium temperatures.  We also show the reflectance from a surface of Re at a pressure of 1 bar at room temperature. The reflectances have been corrected 
for absorption in the diamond. Filled points are raw data and hollow ones are corrected. The uncertainties in the data points are from measurement of the reflectance and the correction procedure and represent random errors. The lines through the SMH data points are fits with a Drude free electron model; the lines through the Re data points are guides to the eye.
A: Judging by https://arxiv.org/abs/1610.01634, the photograph from the microscope is not exactly the only evidence, they also performed reflectance measurement using a spectrometer (see their Figure S5). These two kinds of evidence are closely related, but not identical.
