A proof is useful only when the team is clear about the question it must answer. A quick paste proof can show whether mounted plates fit and register. It cannot be treated as a colour-accurate production sample because the ink is applied by hand and is not metered through the production anilox. When colour, ink laydown or the behaviour of the actual substrate matters, the proofing method has to reproduce more of the press conditions. Decide that before the plates are released, not after the proof has already been shown to a customer.
Start with the decision the proof must support
Write down what the proof will approve. Common questions are whether every plate is present and in the correct orientation, whether the colours fit in register, whether the copy and separations are correct, or whether the printed colour and appearance are close enough for customer approval. These are not the same test.
Heaford separates flexo proofing into two practical methods. A mounter proofer uses acrylic or paste ink on paper to create a physical proof of the mounted plates and their register. A flexo proof press uses the production substrate, sleeves, plates, anilox rollers and production ink. That difference should determine what the proof is allowed to approve.
Use a paste proof to check fit and register
Paste proofing is the faster route when the main concern is mechanical and visual. Water-based acrylic ink is applied with a hand roller and the mounted plates are proofed onto paper. The operator can check plate sequence, image orientation, gross defects, separations, fit and register before the sleeve or cylinder reaches the press.
The method is especially useful for a new mounted set, a difficult multicolour fit or a long production run where finding a misplaced plate on press would be costly. It also gives prepress and mounting a physical record that is easier to review than looking at one register mark through a camera.
Do not ask a paste proof to approve colour
On a paste proof, ink is applied by hand and is not metered by the production anilox. The amount transferred depends on the application and the operator. The paper used for proofing also behaves differently from a film, foil, laminate or labelstock. A colour that looks light, heavy or uneven on the paste proof may not predict the press result.
Mark the proof clearly with its purpose, for example, 'register and content check only'. Do not present it as a contract colour proof. If the customer or production team needs to approve colour, density, ink laydown, fine tonal response or appearance on the final substrate, move to a method that reproduces the relevant production parameters.
Use a wet proof when the material and ink matter
A wet proof uses the production ink and meters it through an anilox. Heaford's flexo proof press is designed to work with production substrates, sleeves, plates, anilox rollers and solvent, water-based or UV inks. This makes it the more suitable method for prototype work, colour evaluation and jobs where the interaction between ink and substrate must be seen before production time is booked.
Match the proof setup to the planned job as closely as the approval requires. Record the substrate batch or specification, ink series and colour, anilox identification, plate and tape construction, sleeve, impression settings and proof speed. If one of these is substituted, state it on the proof. A sample without its conditions is difficult to reproduce or investigate later.
Control the wet-proof setup like a small production run
Inspect the sleeve and plate, confirm the correct anilox and prepare the production ink to the approved condition. For water-based and solvent ink, record the plant's normal viscosity method and temperature; for water-based ink, include pH where it is part of the control standard. For UV ink, confirm the curing arrangement used for the sample. The purpose is to remove avoidable differences between the proof and the planned press run.
Set anilox-to-plate and plate-to-substrate impression deliberately rather than pressing harder until the image looks full. Allow the ink and machine to reach a stable condition, then retain the proof that was actually approved. If density, colour or dot response will be measured, use the same instruments, backing, target and acceptance method that the production team understands.
Keep the approval attached to the exact sample
Give every proof a job number, revision, date and status. Identify whether it is a paste proof for register or a wet proof for production comparison. Note who approved it and what was excluded from the approval. Keep rejected samples as well when they explain a plate correction or a changed colour target.
Send the accepted sample and its setup record with the job. The press operator should not have to guess whether a difference came from an approved artwork revision, another anilox, a changed ink condition or a proof made only to check register. Where the proof is intended for a customer, agree in advance whether it is a visual guide, a measured target or a contract approval.
Choose the proofing method from the cost of being wrong
Not every job needs a wet proof. A routine repeat with approved plates and stable production data may need only the normal mounting checks. A new multicolour plate set may justify a paste proof. A high-value launch, prototype, unfamiliar substrate or colour-critical job can justify a wet proof because the decision depends on production materials and ink transfer.
Royal Coat represents Heaford mounting and proofing technology in India, Bangladesh, Sri Lanka, Nigeria and Kenya. For an application discussion, send the Royal Coat team the press type, web width, repeat range, sleeve or cylinder format, normal substrates and inks, present approval process and the press time currently used for trials. The right system follows the proof you actually need to make.
Questions from production and purchasing teams
What to ask about flexo proofing
Can a paste proof be used to approve colour?
It should normally be used for plate content, fit and register. The hand-applied ink is not metered by the production anilox and the proof paper may not behave like the final substrate.
What makes a wet proof closer to production?
It can use the production substrate, ink, sleeve, plate and anilox, with controlled impression and operating conditions recorded for the sample.
Does every new flexo job need a wet proof?
No. Choose it when colour, ink laydown, prototype appearance or substrate behaviour must be evaluated off press. A paste proof may be enough when the decision is limited to plate fit and register.
What should be written on an approved proof?
Record the job and revision, date, proofing method, materials and key settings, approval status, approver and exactly what the sample is intended to approve.
What information helps specify a proofing system?
Provide the press and web width, repeats, sleeves or cylinders, substrates, ink types, current proofing method, approval requirements and the production time now spent on trials.