Charcoal Under Humidity: Flattening, Fixing and Mounting a Large Drawing
A candidate is making a 1.2 m × 0.9 m charcoal drawing on 200 gsm cartridge paper for a school exhibition that opens in ten days and runs for five days in a covered outdoor corridor. The corridor is open to humid air: forecasts give 85% relative humidity and 30°C, with occasional wind-driven rain. The paper was rolled in a cardboard tube for two days and now shows waves along the long edge; charcoal has offset onto the tracing paper interleaved with it. The candidate applied one light coat of fixative, but the surface still smudges when touched. The remaining budget is HK$250. The school stores 5 mm foam board, acid-free tissue, linen tape and acrylic glazing, but no frame deeper than 2 cm. Only low-VOC fixative may be sprayed outdoors, and the corridor must keep a 1.5 m clear route. The candidate has ten days from today to resolve the problems before installation.
1. Diagnose the two main material problems and explain their likely causes.
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Two problems are visible. The waves along the long edge are cockling: the paper has absorbed moisture unevenly, and rolling in a tube has imposed a curl that the fibres now hold. Cartridge paper is not fully dimensionally stable, and at 85% RH it will expand; the 1.2 m edge exaggerates the movement. The charcoal offset is a pressure-and-fixative problem. Tracing paper in direct contact transfers charcoal under the weight of rolling; one light coat of fixative has bound only the top layer of charcoal, so the surface still smudges. More fixative will help, but over-application can darken the drawing, produce a bloom or make the paper more brittle. The torn margin is not the main issue yet, but it shows that handling is already causing damage. The candidate should treat the paper as a hygroscopic material, not as a rigid board, and separate the flattening problem from the fixing problem.
2. Propose a remediation and mounting plan within the HK$250 budget and the corridor constraints.
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First, unroll the drawing face up on acid-free tissue in a dry room, not in direct sun. Place acid-free tissue over the surface, then blotting paper, then two rigid boards larger than the sheet, and weight evenly. Change the tissue daily; the aim is slow, even drying, not heat. Test the low-VOC fixative on a scrap of the same paper: spray outdoors from about 30 cm in three thin passes, waiting between passes, and check for darkening. Then fix the drawing in the same way. For mounting, use the 5 mm foam board only as a temporary backing, covered with acid-free tissue to create a barrier; hinge the paper at the top with linen tape so it can expand, and use acrylic glazing with foam spacers so the glazing does not touch the charcoal. If the acrylic and clips exceed HK$250, show the work indoors on a wall with the same backing and no glazing rather than risk condensation in the corridor. Keep the 1.5 m route clear and never place the work where rain can blow in.
3. Revise the schedule with a contingency plan for the ten days before installation.
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Work backwards from the opening. Days 1–3: flatten under weight, changing tissue daily. Day 4: test fixative on scrap and check for colour shift. Day 5: apply fixative in thin passes outdoors. Day 6: mount on the prepared backing and check the hanging height. Day 7: install, with a label that states the medium and the fragility of charcoal. Days 8–9: buffer for re-fixing or re-mounting. Day 10: opening. The contingency is important: if the waves persist, do not crop the sheet or iron it; increase the weight and drying time, and if necessary change the display location to a drier indoor wall. If the fixative darkens the drawing, stop and accept a more fragile surface rather than over-fix. The schedule should also include photographing the work before installation, because the corridor is a risky display environment.