Paint by Numbers Quality Guide: Canvas, Acrylic Paint & Brush Specs
Written by the production and QC team at Art Painting by Numbers, Tianjin · Updated October 2026 · 13 min read
Three components decide whether a customer finishes a paint by numbers kit or abandons it: the opacity of the acrylic paint, the elasticity of the brush filament, and the coating of the canvas. Everything else — box finish, insert design, canvas size — affects how the product sells. These three affect whether it works.
None of them are visible in a product photograph, which is exactly why they get cut first when a buyer asks a supplier to hit a lower price. This guide is the specification sheet we use internally, written so a buyer can quote it back to any factory and get a comparable answer.
Canvas
The canvas carries the printed numbered outline, which is the reference the painter depends on for hours. Two failure modes matter: numbers bleeding when wet paint touches them, and the surface not holding acrylic properly so colour lifts or beads.
| Grade | Material | Weight | Coating | Use for | Relative cost |
|---|---|---|---|---|---|
| Economy | Poly-cotton blend | 230–260 gsm | Single-side light primer | Mini kits, promotional items, low price points | 1.0× |
| Standard | Cotton-blend | 280–320 gsm | Double-side acrylic primer | Most retail kits, 20 × 30 to 40 × 50 cm | 1.25× |
| Premium | Pure cotton | 340–380 gsm | Triple-coat, archival-grade | Premium and gift ranges, framed kits | 1.6× |
| Artist | Linen | 380–450 gsm | Triple-coat with sizing | Large format, high retail price, art-market positioning | 2.4× |
What to specify: at least 280 gsm cotton-blend with a double-side acrylic primer for any retail kit above 20 × 30 cm. Below that weight the canvas wrinkles when paint is applied and the print registration shifts visibly.
What to check on a sample: brush a wet stroke of dark paint directly across a printed number and wait two minutes. If the number is still legible through the dried paint, the coating is right. Then flex the canvas sharply — a properly primed surface cracks at the fold rather than flaking.
Print quality on the canvas
- Line weight — 0.3–0.5 mm for main outlines, 0.2 mm for internal divisions. Thinner than 0.2 mm disappears under one coat of paint.
- Number size — 4 mm minimum for a 40 × 50 cm canvas; 5–6 mm for an accessible or senior range. This is the most common complaint from painters over fifty and the cheapest thing to fix.
- Outline colour — light grey, not black. Black outlines require two coats of paint to cover and produce a muddy result in pale areas.
- Registration — within ±0.5 mm. Misregistration puts a number in the wrong segment, which is unrecoverable for the painter.
- Resolution — source artwork at 300 dpi at final print size. Anything less produces soft number edges that bleed.
Acrylic paint
Paint is where cheap kits fail most visibly, because the failure happens in the customer's hands, hours after delivery, and they blame themselves before they blame the product.
Opacity and pigment load
The critical specification is single-coat coverage over a printed dark outline. Low-pigment acrylic needs three coats, which means the painter runs out of paint two thirds of the way through — the most common cause of an unfinished kit and a bad review. Ask a supplier for the pigment load as a percentage, or simply test it: paint one coat over a black outline on the sample and hold it up to daylight.
Viscosity and open time
Paint should flow from a fine brush without dripping and stay workable for 8–12 minutes on the palette. Too thick and it will not level in small segments; too thin and it runs outside the outline. Fast-drying formulations frustrate blending in sky and water areas. Our standard formulation is a medium-viscosity acrylic with a retarder that keeps open time around ten minutes.
Pot size, sealing and shelf life
| Pot volume | Suitable canvas | Colours typical | Notes |
|---|---|---|---|
| 2 ml | 10 × 15 and 20 × 20 cm | Up to 18 | Tight for darker palettes; specify 3 ml if coverage matters |
| 3 ml | 20 × 30 to 40 × 50 cm | 18–30 | Our standard. Balances cost, coverage and parcel weight |
| 5 ml | 40 × 50 cm and above | 24–40 | Use for large skies, dark backgrounds or high-coverage designs |
| 8 ml | 50 × 65 cm and above | Any | Premium and large-format ranges |
Sealing is what determines whether paint arrives wet. Every pot must be foil-sealed under the screw cap and the strip vacuum-packed. Unsealed pots lose moisture through the cap thread in transit and arrive as a rubbery plug. Target shelf life is 24 months sealed, 3–6 months once opened — worth printing on the instruction card, because painters who leave a kit open for a year and then complain have a legitimate grievance they cannot diagnose.
Safety
Water-based, non-toxic acrylic is the baseline. Where you sell to children or into regulated markets, specify third-party testing: EN71-3 for migration of heavy metals in the EU, ASTM F963 and CPSIA for lead and phthalate limits in the United States, and REACH for chemical restrictions. Reports should be issued in your company name where a retailer or marketplace requires it. We arrange testing through accredited laboratories and supply the reports with your shipment — see our standards and compliance section.
Brushes
The brush is the component customers mention most often in reviews, positively and negatively, because it is the thing their hand holds for three hours.
| Specification | Economy | Standard | Premium |
|---|---|---|---|
| Filament | Standard nylon | High-elasticity nylon | Sable-blend or tapered nylon |
| Tip recovery | Splays permanently within 10 minutes | Returns to a point after pressure | Holds a point through a full session |
| Ferrule | Aluminium, crimped | Aluminium, double-crimped, corrosion resistant | Nickel-plated, seamless |
| Handle | Painted wood, short | Kiln-dried hardwood, balanced length | Lacquered or laser-engraved hardwood |
| Shapes supplied | 2 round | 3 — flat, round, detail | 4–5 — flat, round, detail, liner, fan |
| Cost impact per kit | baseline | +$0.06 | +$0.18 |
The single best upgrade you can buy is moving from standard nylon to high-elasticity filament. It costs about $0.06 per kit and eliminates the most frequent negative review in this category. If you sell at a premium price point, add a tapered liner brush for fine detail — another $0.12 that experienced painters notice immediately.
How to test: wet the brush, load it with paint, press firmly onto a hard surface for five seconds, release, and watch the tip. A good filament snaps back to a point within two seconds. A poor one stays splayed and never recovers, which means the painter cannot do detail work for the rest of the kit.
Frames, packaging and the rest
- Stretcher bars — kiln-dried pine, moisture content below 12%, mitred and stapled. Green or unseasoned wood warps in transit and in a heated home, which pulls the canvas out of square.
- Box board — 300–350 gsm for a standard printed box, 1,200 gsm greyboard wrapped for a rigid gift box. Corrugated E-flute where the kit ships direct to a consumer without an outer carton.
- Inserts — moulded pulp or folded card to stop components moving. Movement causes paint pots to crack open, which is the most common transit damage claim.
- Reference card — printed at 200–250 gsm, matte laminated so paint drops wipe off. A gloss-laminated card holds fingerprints and glare.
- Export carton — double-wall corrugated, 5-ply, with the design item code and quantity printed on two adjacent faces so a warehouse can identify it without opening.
Carton dimensions and container planning figures are on the wholesale page.
Where it is safe to economise
Hitting a target price is a legitimate goal. These cuts do not damage the painting experience:
- Reducing colour count from 30 to 22 — often improves the experience, because segments get larger
- Rolled canvas instead of framed — the largest single cost saving, and most buyers frame their own finished work anyway
- Kraft mailer instead of a litho-printed box, with a printed sleeve for shelf impact
- Two brushes instead of three, provided one is a good detail brush
- Standard cotton-blend canvas instead of pure cotton, for canvases under 40 × 50 cm
These cuts damage it: unsealed paint pots, standard-nylon brushes on a kit with fine detail, sub-280 gsm canvas above 30 × 40 cm, black printed outlines, and numbers smaller than 4 mm on a full-size canvas. Each one produces a review that says the product was impossible to finish — and the reviewer will be right.
A specification you can send to any supplier
Copy this into an enquiry and you will get comparable quotes instead of vague ones:
Canvas: cotton-blend, 300 gsm, double-side acrylic primer,
40 x 50 cm, rolled with protective interleaving
Print: light grey outlines 0.3-0.5 mm, numbers 4 mm minimum,
registration within 0.5 mm, 300 dpi source
Paint: water-based acrylic, single-coat coverage over printed outline,
medium viscosity, 10-minute open time, 3 ml pots,
foil-sealed and vacuum-strip packed, 24 colours
Brush: 3 pcs high-elasticity nylon - flat, round, detail;
double-crimped aluminium ferrule; kiln-dried hardwood handle
Cards: colour reference sheet 250 gsm matte laminated;
line-art guide card; printed thank-you card with QR
Pack: kraft mailer with printed full-wrap sleeve;
folded card insert to immobilise pots
QC: AQL 2.5 major / 4.0 minor, inspection report with photographs
Terms: FOB Tianjin, 500 sets, lead time from approved artwork
Send that to us and we will quote within 24 hours. Send it to three suppliers and you will learn a great deal from which ones cannot answer parts of it — a point developed in how to vet a paint by numbers supplier in China.
Frequently asked questions
What canvas weight is best for paint by numbers?
280–320 gsm cotton-blend with a double-side acrylic primer for retail kits between 20 × 30 cm and 40 × 50 cm. Below that weight the canvas wrinkles when paint is applied and print registration shifts; above 380 gsm you are paying for artist-grade material that hobby painters will not notice.
Why does paint in some kits arrive dried out?
Almost always because the pot was not foil-sealed under the cap. Moisture escapes through the cap thread during weeks of transit and the paint sets into a plug. Specify foil-sealed, vacuum-strip-packed pots and check the seal when your sample arrives — it takes ten seconds and prevents the most avoidable complaint in this category.
How many colours should a 40 × 50 cm kit have?
Between 20 and 28. More colours means smaller segments and more pots, each with less paint, which increases the risk of running out and of pots drying between sessions. A 40-colour canvas looks impressive in a listing thumbnail and is significantly harder to finish.
Are the paints non-toxic and safe for children?
Our acrylic paints are water-based and non-toxic as standard. For a product marketed to children, specify third-party testing to EN71-3 in the EU, ASTM F963 and CPSIA in the United States, and REACH for chemical restrictions, and grade the packaging accordingly. Untested goods should be sold as adult craft products, age 14 and over.
What is the cheapest upgrade with the biggest effect on reviews?
High-elasticity nylon brush filament, at about $0.06 per kit. Brush quality is the component customers describe most often in reviews, and standard nylon that splays permanently within ten minutes is the most common specific complaint we see in low-cost kits.
Order a sample and test it yourself
Every check in this guide takes one evening with a sample kit. Sample cost is refunded against your first production order. Tell us your specification and destination and we will quote within 24 hours.