Three to four analyses of water concentrations were obtained by FTIR spectroscopy in six glasses: the mean values range from 5.95 to 6.15 wt%, and individual analyses in a single glass are within ±0.1 wt% (Table  1 ).

The run conditions and the main results are summarized in Table  1 ..

The 2D bubble size distributions (BSD) were converted to 3D BSDs to estimate the 3D mean bubble size and the number of bubbles per unit volume of liquid (Table  1 ).

In the 1,000 kPa/s series, the samples quenched at P_F  ≥ 64.5 MPa showed a bubble-free core, whereas those quenched at P_F  ≤ 59.7 MPa had a vesiculated core (Table  1 ).

In the 27.8 kPa/s series, the nucleation pressure is bracketed by the experiments Hem 9 and Hem 4 (at P_F  = 67.7 and 70.1 MPa, respectively; Table  1 ).

An important evolution of the mean 3D bubble size, D , is observed with decreasing pressure (Table  1 ).

With decreasing pressure, vesicularity increases from a few percent just below the nucleation pressure ( V  = 2.6 vol% at P_F  = 59.7 MPa in the 1,000 kPa/s series) up to 69 vol% at P_F  ≈ 20.5 MPa (Table  1 ; Fig.  4 ).

For comparison, we computed the equilibrium vesicularity as a function of pressure for Güney Daği composition at 800°C and for a total water content equal to 6 wt% (Table  1 ).

To evaluate how close to equilibrium degassing proceeds in our decompression experiments, we measured the water contents in glasses of six samples from the 27.8 kPa/s series and two samples from the 1,000 kPa/s series (Table  1 ).

The water contents were measured by FTIR spectroscopy in six experiments of the 27.8 kPa/s series ( empty circles ), and two experiments of the 1,000 kPa/s series ( solid circles ); the error bars correspond to twice the standard deviation (see Table  1 ).

(1) The water content in sample Hem 4 (≈6.1 wt% H ₂ O, P_F  = 70.1 MPa; Table  1 ), quenched just above the nucleation pressure, is equal to the initial water content.

For comparison, X_SAT  = 3.5 wt% at 800°C and 70.1 MPa (see the last column in Table  1 ).

X _SAT  = 3.19 wt%, that is Δ X  ≈ 2.1 wt% (Table  1 ).

This observation is in agreement with textural measurements: the vesicularities at P_F  ≤ 40–50 MPa approach equilibrium values in the two decompression series, and are even slightly larger and closer to equilibrium in the 1,000 kPa/s series (Table  1 ; Fig.  4 ).