The rule fits in one sentence: most Vision Picturale processes call for a negative chart. Two exceptions call for a positive interpositive: resinotype and screen printing. This page documents the rule, its physical origin for resinotype, the full table by process, and where this setting lives in Calibration Flow.
To calibrate a digital printer itself (compensating for its non-linear response): negative chart, just like for the standard negative processes.
#Comparison table
| Process | Chart polarity | Why |
|---|---|---|
| Cyanotype | Negative | Standard convention of contact-exposure alt-processes |
| Aquaprint Monochrome | Negative | Same — gum bichromate |
| Aquaprint Sanguine | Negative | Same |
| Aquaprint CMYK Four-Color | Negative | Same (one negative per channel) |
| Bromoil | Negative | Same |
| Carbon Mono (only VP kit available) | Negative | Same |
| Color carbon (if practiced, CMYK four-color like Aquaprint) | Negative | Same (one negative per C, M, Y, K channel) |
| Gumoil | Negative | Same |
| Resinotype | Positive (interpositive) | Exception: pigments settle on the black areas of the negative (non-exposed areas) |
| Screen printing | Positive (interpositive) | Exception — see Screen printing film for the full process |
| Printer calibration | Negative | The printer is treated as a tonal chain to compensate, like a standard negative process |
#Where this is set in the app
In Calibration Flow, the chart (the Control strip on the Negative screen — see Which test chart to choose) has no positive/negative switch of its own. It follows whichever mode you chose for the whole negative: generate in Positive or Negative, and the chart automatically takes on the same polarity as the rest of the image, with no separate setting. So picking the right generation mode for your process — the rule in the table above — sets the chart's polarity at the same time.
On the site's 21-step chart, independent of the app, that same choice is a dedicated selector: positive or negative.
The Color Venn chart (dedicated page) doesn't have this setting: it tests color ink overlap, not a grey scale, so the positive/negative question doesn't apply to it.
#When to use a negative chart
This is the general case. Cyanotype, Aquaprint (all variants), bromoil, carbon (all variants), gumoil all work this way. For these processes, the source image printed on an inkjet transparency is in negative polarity — the standard convention for any alt-process contact print.
For calibrating a digital printer (Calibration Flow is also used for this, independently of any alt-process): negative chart as well. The printer has its own non-linear response, handled mathematically like a standard negative process.
#When to use a positive chart (interpositive)
For resinotype and screen printing.
The reason is physical for resinotype. The chemistry (pigmented gelatin and sensitizer, proprietary VP resin) behaves differently from the other hardening processes:
In an Aquaprint or a carbon, pigments stay where UV light hardened the gum or the gelatin — the exposed areas (clear transparency = light passes = chemistry hardens). The standard negative therefore yields a positive print.
In a resinotype, it's the opposite: pigments cling to the non-exposed areas, the ones UV light did not reach — which correspond to the opaque (black) parts of the negative. For the print to resemble the original image, you have to present the chemistry with an inverted image: a positive interpositive.
For screen printing, the mechanism comes down to the film and emulsion specific to the process — see Screen printing film for the full detail. Keep the rule in mind: screen printing = positive, same as resinotype.
#Color carbon and Aquaprint Four-Color — the same logic
The table above treats the color processes the same way (negative chart) because they follow the same scheme in Calibration Flow — the app has no three-channel mode:
- Aquaprint CMYK Four-Color: four separate negatives (Cyan, Magenta, Yellow, Black), each in a negative chart. Recommended print order: Yellow → Cyan → Magenta → Black. Each layer is a gum layer with its own pigment.
- Color carbon: Calibration Flow's four-color mode always generates 4 channels (Cyan, Magenta, Yellow, Black). A color carbon calibration would follow the same scheme as Aquaprint, with a pigmented-gelatin transfer per layer instead of a gum layer.
As of today, Vision Picturale only sells the Carbon Mono kit; the color chemistry isn't finalized. An Aquaprint calibration generates four correction curves (one per CMYK channel); a color carbon calibration would do the same.
For both processes, registration marks are needed to align the layers.
#Key points
| Element | Value |
|---|---|
| Format (Negative screen's chart) | 25 patches in a 5×5 grid, from pure white to maximum black, plus an always-present gradient band |
| Negative polarity | Patches ordered white to black, read in the reverse direction of the normal image |
| Positive polarity (interpositive) | Patches ordered white to black in the normal readable direction |
| Setting in the app | No dedicated setting: it follows the Negative/Positive mode chosen for the whole negative |
| Processes concerned | Every VP process in negative — resinotype and screen printing alone in positive |
#Founder's notes
Resinotype has its polarity inverted because of a quirk of the resin + pigmented-gelatin chemistry. It's a detail that's easy to forget — hence a whole page underlining it. During Calibration Flow's first months, several practitioners reported resinotypes "coming out backwards" to us. When we dug in, it was always the same point: they'd used a negative chart like for the other processes. The "everything in negative except resinotype and screen printing" rule is there so we no longer have to dig in every time.