Context : The first ionization potential ( FIP ) bias is currently used to trace the propagation of solar features ejected by the wind and solar eruptions ( coronal mass ejections ) .
The FIP bias also helps us to understand the formation of prominences , as it is a tracer for the solar origin of prominence plasma .

Aims : This work aims to provide elemental composition and FIP bias in quiescent solar prominences .
This is key information to link these features to remnants of solar eruptions measured in-situ within the heliosphere and to constrain the coronal or photospheric origin of prominence plasma .

Methods : We used the differential emission measure technique to derive the FIP bias of two prominences .
Quiet Sun chromospheric and transition region data were used to test the atomic data and lines formation processes .
We used lines from low stage of ionization of Si , S , Fe , C , N , O , Ni , Mg , and Ne , constraining the FIP bias in the range 4.2 \leq \log T \leq 5.8 .
We adopted a density-dependent ionization equilibrium .

Results : We showed that the two prominences have photospheric composition .
We confirmed a photospheric composition in the quiet Sun .
We also identified opacity and/or radiative excitation contributions to the line formation of a few lines regularly observed in prominences .

Conclusions : With our results we thus provide important elements for correctly interpreting the upcoming Solar Orbiter/SPICE spectroscopic data and to constrain prominence formation .