Which test chart to choose?

A calibration test chart is never a single object — it exists in variants suited to different contexts. One version for positive processes like resinotype, one version for every other process in negative. A plain version for everyday diagnosis, a version augmented with a continuous gradient for fine reading. A high-resolution version for printers that render dithered patterns better than solid flats.

Calibration Flow offers six variants in the menu. You choose the one that matches your process and your printer. Once chosen, you download the PNG file, print it on an inkjet transparency, and start your test-chart print. This page documents the six variants and tells you which one to take for your case.

#The six variants

Plain positive chart. Grid of grey patches ordered in positive polarity (dark patches correspond to dark areas on the print). Used for resinotype — the only process that calls for this polarity.

Positive chart with gradient. Same patch grid, plus a bonus continuous gradient band. The band lets you see the smooth tonal transition in addition to the discrete steps. For resinotype as well.

Positive A4 landscape high-resolution chart. A format suited to A4 landscape paper, at higher print resolution (300 dpi vs 150 dpi for the plain versions). Bonus: Floyd-Steinberg or halftone bitmap dithering is built directly into the chart — useful for printers that render solid grey flats poorly.

Plain negative chart. Negative polarity for every process other than resinotype: cyanotype, platinotype, palladium, Van Dyke, carbon, gum bichromate (Aquaprint), bromoil, gumoil. It's the most-used chart. For printer calibration itself: negative as well.

Negative chart with gradient. Same, with the continuous gradient band added.

Negative A4 landscape high-resolution chart. Same in high resolution + built-in dithering. For the same reason as the positive version — when your printer struggles with flats.

#How to choose

Answer two questions:

Which polarity? If you're calibrating a resinotype, take a positive version. Otherwise (every other process and printer calibration), take a negative version. See Positive or negative chart for the full reasoning.

Which version (plain, gradient, A4 high-resolution)? Three cases:

• Plain: suited to most cases, standard format. If you're starting out or your previous test chart came out well, stay on Plain.
• With gradient: adds the continuous band. Useful if you want to compare the reading by discrete steps to that of a continuous gradient — for instance to spot a non-linear response threshold in your chemistry.
• A4 landscape high-resolution: choose it if your printer renders grey flats poorly (you see banding or stray patterns on the test-chart prints), or if you're calibrating a carbon or an Aquaprint where dithering is explicitly recommended.

#Why this diversity

Because polarity depends on the process. Resinotype works through pigment adhesion in the non-exposed areas — it calls for literally the inverse of every other process. A single polarity wouldn't be enough to cover the full ecosystem.

Because printers vary. A high-end Epson SureColor renders grey flats perfectly. A mid-range consumer printer can introduce banding or stray patterns when it prints a 50% grey flat on a transparency. Having a variant with built-in dithering saves you from hand-tuning the print driver settings — the app generates a chart directly that most printers can reproduce correctly.

Because the continuous gradient adds a complementary reading. The discrete patches give you 25 precise measurements. The gradient gives you a continuous transition that visually reveals non-linearities the 25 patches might mask. Having both side by side enriches the diagnosis.

#When you don't need all this

For an occasional cyanotype calibration. Take the plain negative chart, don't ask any further questions. It's the most common and the simplest case.

For experienced users who want a custom chart. Non-A4 format, different patch count, square format — none of the six variants fits. Custom chart creation isn't available in the app yet; when this feature is integrated, it will be documented on Create a custom test chart.

If you always reuse the same chart between calibrations. Keep the PNG downloaded once and reuse it. No need to go back into the menu to regenerate it every session.

#Key points

#The test

Choose the variant that matches your current process. Download the PNG, print it on an inkjet transparency without color management (see Printing without color management). Lay the transparency on a white sheet and examine it in daylight: you should see 25 grey patches spread out evenly, from transparent white to opaque black. If the chart you printed doesn't look like that, either you downloaded the wrong variant, or your print has a problem.