Inkwash

What it does

Inkwash is a drawing app for iPad and drawing tablets that simulates watercolor painting using fluid dynamics. Users draw with pen strokes, then apply a simulated waterbrush that pulls ink washes across the canvas. The app runs in a web browser as a single HTML file and uses WebGL2 shaders to model water flow, pigment density, and settling behavior frame-by-frame.

Who it is for

The app targets digital artists and sketchers who want to replicate the feel of traditional watercolor and ink techniques on tablets. It suits people who enjoy nature journaling and prefer the imperfect, spontaneous quality of wet media over precise digital control. The creator developed it based on their own practice of pairing pen linework with waterbrush washes for fast figure drawings and sketches.

Pricing

The site does not show prices.

How it stands out

Inkwash uses a physics-based approach rather than preset brushes. The engine simulates three separate states—ink pigment, settled color, and water wetness—across floating-point texture layers. Water velocity and pressure are computed each frame to create organic flow behavior. The app stores optical density rather than final color, allowing the rendering to calculate how light interacts with pigment and paper. Every interactive demo on the homepage runs the actual engine at miniature scale, showing users the fluid simulation in action. The creator built it using Claude Fable 5, an AI coding model, and has published the prompts used to generate the code.

What a founder should check

A competitor should verify how many other tablet drawing apps already offer fluid-based watercolor simulation—tools like Procreate, Adobe Fresco, and Rebelle have mature water-physics features with years of refinement. Second, test whether the browser-based delivery creates switching costs or friction compared to native apps, especially regarding performance, file handling, and integration with iPad workflows. Third, examine whether the single-file architecture and open-source approach (the code appears readable in the browser) create a sustainable business model or if the real value lies in community and tutorials rather than the software itself.