This article presents a novel, high-performance, screen-printable zinc (Zn)-based ink and a chemical sintering process that significantly improves long-term air stability. The ink formulation combines micro- and nanoparticles, enhancing electrical conductivity—up to 10 times compared to microparticle-only inks. Micro-fibrillated cellulose (Exilva) is used as a sustainable binder, aligning with eco-friendly electronics initiatives. Besides the formulation, the benefit of a multistep chemical sintering approach, based on the sequential immersion of the printed structures in acetic acid solution, is demonstrated. If with a more conventional one-step acetic acid sintering treatment a conductivity of ≈3.18 × 10⁵ S m−¹ can be achieved, the use of the multi-step process further enhances both conductivity, increasing conductivity ≈2.6 times to ≈8.37 × 10⁵ S m−¹ (sheet resistance 0.06 Ω □−¹), it is the highest reported value achieved through chemical sintering—just 20 times lower than bulk Zn (≈16.6 × 10⁶ S m−¹). Importantly, the ink, following the proposed chemical sintering and without encapsulation also exhibits outstanding air stability, maintaining functionality with only an ≈11% increase in resistance after 6 months in ambient conditions (40–60% RH). By offering superior durability, flexibility, and, most notably, unprecedented air stability, this Zn-based ink presents a significant advancement for sustainable and flexible electronics.