Historic paint analysis as evidence for redecoration

Paint analysis answers a narrow question well: what was on this surface, in what order, and roughly when. It does not tell you what colour a room should be painted now. The distinction matters because owners commission architectural paint research expecting a palette and receive a stratigraphy, and conservation officers receive a stratigraphy and are asked to accept it as justification for a scheme the analysis does not actually support.

Used properly, the evidence is strong. A cross-section through nineteen generations of paint on a door architrave, with a dirt layer above the fourth generation and chrome yellow in the sixth, tells you more about a room's history than any documentary source is likely to.

What analysis can establish

The core output is a sequence. Samples are taken, mounted in resin, polished to expose a cross-section and examined under reflected visible and ultraviolet light, which separates the layers and distinguishes media. From there the analyst can identify pigments by polarised light microscopy and, where needed, by laboratory instrument techniques, and can characterise the binding medium.

Relative dating comes from pigment chronology. The introduction dates of a number of pigments are well established, which is what makes the method work: Prussian blue from the early eighteenth century, chrome yellow from the early nineteenth, artificial ultramarine from the late 1820s, and titanium white not before the twentieth century. A layer containing titanium white cannot be Georgian, whatever the room's date.

What else the work can establish, in descending order of reliability:

• The number of decorative generations and their order
• Whether an original scheme survives on the surface sampled
• The presence of decorative treatments such as graining, marbling, gilding or stencilling beneath later paint
• Approximate dates for particular generations, from pigment and medium evidence
• Original colours, with caveats about the alteration of the medium and the pigments over time
• Whether different elements in a room were decorated as one scheme or at different times

That last point is often the most useful for a redecoration proposal. Establishing that the joinery, the plaster and the chimneypiece were painted as a single scheme in a particular generation is a stronger basis for a unified treatment than a colour match alone.

Where to take the samples

Sample location decides the quality of the result, and the analyst should choose the locations rather than being handed a set of scrapes taken by a decorator.

Protected positions retain the fullest sequence, because they escaped the scraping, washing and stripping that removed early layers from exposed faces. In practice that means beneath later mouldings and beads, behind shutters and in shutter boxes, in rebates and reveals, on the returns of architraves, above picture rails and cornices, on the backs of doors in the hinge rebate, and in the angle between skirting and floor.

Avoid prominent surfaces. A sample site is a small area of damage, and although a well-taken sample is a few millimetres across, every sample location should be recorded and the number kept proportionate to the question being asked.

Record each location on a measured drawing or an annotated photograph, numbered to match the report. A report whose sample locations cannot be identified on site afterwards is worth considerably less, because nobody can check it or extend it later. Where historic maps and documentary sources are also being used, cross-referencing the paint sequence against the dates established by using historic maps in an assessment tightens both.

Reading a stratigraphy report

The report will present a table of layers for each sample, and the first thing to establish is whether the analyst is reporting layers or generations. A single decorative generation usually comprises several layers, a primer, one or more undercoats and a finish, and counting layers as schemes multiplies the apparent history by three or four.

Soiling layers are the most informative feature and the most frequently overlooked. They distinguish a generation that was lived with from one applied and repainted within a season, which is what separates a scheme worth reinstating from a passing undercoat.

Read the interpretation section with the same care as the data. A competent report distinguishes clearly between what the samples show and what the analyst infers, and uses hedged language for the latter. Where it does not, ask.

Using the results to justify a scheme

Internal redecoration of a listed building does not usually need listed building consent, because repainting a surface in the ordinary way does not affect the character of the building as one of special architectural or historic interest. The position changes where a historic decorative scheme survives and would be covered, where the works involve removing paint from historic fabric, or where the proposal alters the perceived hierarchy of an interior of real interest.

So the analysis has two uses in a consent application. It can establish that nothing of interest survives on the surfaces to be painted, which removes the objection. Or it can establish what does survive and inform a proposal that retains or reveals it.

Where a scheme is proposed on the basis of the analysis, be explicit about the chain of reasoning in the Heritage Statement: what the samples showed, which generation is being referenced, how the colour was matched and what allowance was made for the alteration of the original, and what will happen to the surviving earlier layers. Covering an early scheme with a reinstatement of a later one is a decision that needs stating rather than assuming.

Paint removal is the part that attracts refusals. Stripping to reveal a scheme destroys everything above it, and the proposal has to justify that loss on the same harm tests as any other removal of historic fabric. Exposure windows, small areas left uncovered and recorded, are often the better answer.

The limits of the evidence

Four limits are worth stating in any report that will be read by a decision maker.

Samples are point evidence. A sequence established on one architrave does not prove the same sequence on the opposite wall, and the number of samples determines how far the conclusions can be generalised.

Early layers may be gone. Victorian and twentieth century practice frequently involved burning off or stripping joinery, and distemper on plaster was routinely washed off before redecoration, so the absence of an early scheme is weak evidence that there was never one.

Colours have changed. Oil media yellow with age, some pigments fade and others darken, and a layer examined in cross-section is seen in a condition different from the one it had when fresh. Reconstructing an original colour therefore involves judgement, and a report that offers a confident colour reference without discussing that judgement is overstating its case.

And the method dates layers, not rooms. Pigment chronology gives a date after which a layer must have been applied, not the date it was applied.

Fees, turnaround and briefing the analyst

Fees depend on the number of samples and the depth of analysis, since cross-section microscopy on a dozen samples is a different exercise from full pigment and media identification across a whole interior. Ask for a written quotation that states the number of samples included, the techniques to be used, whether colour matching is included, and what the report will contain.

Laboratory turnaround is measured in weeks rather than days, so the work has to be commissioned early enough to inform the design. The common mistake is commissioning it after the application has been submitted, when the officer has already asked for it, which adds the turnaround to the determination period.

Brief the analyst with a question rather than an instruction to analyse. Ask whether an original scheme survives on the principal joinery, or whether the panelling and the cornice were decorated together, and the sampling strategy will follow from it.

Recording before the decorators arrive

Whatever the analysis concludes, record the surfaces before anything is done to them. A photographic record keyed to a plan, taken in consistent light with a colour reference in shot, costs very little and is the only version of the room as found that will exist afterwards.

Where the interior is of a grade that warrants it, or where a condition requires it, Historic Building Recording to the appropriate level provides a fuller record, and the paint analysis report should be appended to it rather than filed separately. Retain the sample archive, label it with the locations, and keep it with the building's records. The same principle that applies to salvaged materials and the honesty of repair applies here: the evidence is only useful if the next person can find it and trust it.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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