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We follow-up on a previous finding that AGB Mira variables containing the3DUP indicator technetium (Tc) in their atmosphere form a different sequence ofK-[22] colour as a function of pulsation period than Miras without Tc. A near-to mid-infrared colour such as K-[22] is a good probe for the dust mass-lossrate of the stars. Contrary to what might be expected, Tc-poor Miras showredder K-[22] colours (i.e. higher dust mass-loss rates) than Tc-rich Miras ata given period. Here, the previous sample is extended and the analysis isexpanded towards other colours and dust spectra. The most important aim is toinvestigate if the same two sequences can be revealed in the gas mass-lossrate. We analysed new optical spectra and expanded the sample by including morestars from the literature. Near- and mid-IR photometry and ISO dust spectra ofour stars were investigated. Literature data of gas mass-loss rates of Mirasand semi-regular variables were collected and analysed. Our results show thatTc-poor Miras are redder than Tc-rich Miras in a broad range of the mid-IR,suggesting that the previous finding based on the K-[22] colour is not due to aspecific dust feature in the 22 micron band. We establish a linear relationbetween K-[22] and the gas mass-loss rate. We also find that the 13 micronfeature disappears above K-[22]~2.17 mag, corresponding to $\dot{M}_{\rmg}\sim2.6\times10^{-7}M_{\sun}yr^{-1}$. No similar sequences of Tc-poor andTc-rich Miras in the gas mass-loss rate vs. period diagram are found, mostprobably owing to limitations in the available data. Different hypotheses toexplain the observation of two sequences in the P vs. K-[22] diagram arediscussed and tested, but so far none of them convincingly explains theobservations. Nevertheless, we might have found an hitherto unknown butpotentially important process influencing mass loss on the TP-AGB.

Interplay between pulsation, mass loss, and third dredge-up: More about Miras with and without technetium