by changing the container 54 see fig6 the new pen tip 22 which is saturated with ink or ink thinner is air tight enclosed in this container by means of the puncturable plastic cover 56 the old pen tip can be removed from the pen nib 14 after its notches of the container 54 are clicked beyond the rim 60 of this tip a securing of the new pen tip is accomplished by the following 1 the sharp edges 62 of the nib locally punctures the plastic cover 56 and 2 a complete opening of this punctured seal is obtained by means of the lower end of the nib whereby remnants of this cover are urged against the inner wall of the container see fig4 the ink buffer unit 20 in fig7 and 8 also contains the cleaning wire weight 70 and cleaning wire 72 which extends through the tip 22 furthermore it is provided with an upward extending cleaning wire 74 which extends through the injection tube 18 enabling a perfect transport of ink 46 through this tube by means of the changes of the pen position during pen use with longitudinal displacements of the ink buffer unit and consequently of this wire 74 the sealing of the pen interior by means of the protective cap 48 is perfect.