Selective UV Varnish - Special Effects in Offset Printing

Selective UV varnish - magic for some, a headache for others. If you belong to the latter group, this article is just for you. I'll explain not only how to prepare a file for UV varnish, but also why some things simply won't work, even if you really wanted them to.

Let's start with the basics, because it's important. UV varnish is not ordinary ink - it's a special varnish cured with UV rays. It's applied after printing the four CMYK colors, as a separate process. And here's the first surprise - UV varnish has no color of its own. It's transparent. This means its effect depends on what it lies on.

UV Varnish Physics - Why It Shines and Why Sometimes It Doesn't

Before we get into the technicalities of file preparation, it's worth understanding how UV varnish actually works. It's not just a glossy addition - it's a layer that has its own thickness, texture, and optical properties.

UV varnish is applied by screen printing or flexographic technique directly on the offset press. This means the sheet passes through an additional varnishing unit, where a special forme (similar to a screen in screen printing) applies varnish only in selected areas. Hence the name - selective varnish, because it doesn't cover the entire surface.

After application, the sheet goes under UV lamps, which cure the varnish in a few seconds. The process is spectacular - liquid varnish suddenly hardens and gains gloss. But here's where the trap lies. Varnish is not infinitely thin - it has a thickness of about 8–12 microns. This may seem small, but with small elements it makes a difference.

UV Varnish Mask - Not Every File Is Suitable

Preparing a mask for UV varnish is not copying a layer from graphics. It's a separate file that must meet very specific technical requirements. And here the real fun begins, because most errors in UV varnish result from incorrectly prepared masks.

The mask must be saved as 100% black (C=0 M=0 Y=0 K=100). Not 99%, not 98%, not "very dark gray". Exactly 100% K. Why? Because the machine treats the mask as a binary instruction - varnish either is there or it isn't. Intermediate values cause errors, show-through, or uneven coverage.

I've seen files where the designer prepared a mask as a gradient from 0% to 100% black, thinking the varnish would "lighten" toward the edges. This won't work. UV varnish has no halftones - where there's a black mask, there will be varnish. Where there isn't - there won't be. Period.

Technical Limitations - Where Physics Beats Dreams

Here we come to the part nobody likes - limitations. Selective UV varnish has its physical limits, which result from the application technology and properties of the varnish itself.

First rule - minimum line thickness is 1 point (about 0.35 mm), but 2 points are recommended. Thin lines simply won't print evenly. The screen printing forme has its limitations, and thin varnish can "spread" during application.

Second rule - text for UV varnish should be minimum 14 points high, but 18 points is a safe choice. Small fonts with thin strokes will look illegible or may not print at all. And if you're using a font with very thin elements (like modern sans-serif), raise the limit to 20–22 points.

Third rule - minimum size of varnished element is about 4–5 mm. Small dots, fine details, or thin ornaments may not work. This isn't a matter of the printer's ill will - it's the physics of the process. Varnish must have somewhere to "stand" and spread evenly.

There's another issue rarely discussed - registration tolerance. UV varnish is an additional pass through the machine, so it can shift relative to the print by ±0.3 to ±2 mm, depending on the print shop and technology. This means perfectly fitted varnish to text edges may "go" beyond the letter or not cover it completely.

Varnish at Edges and Scoring

If you're planning UV varnish on a product that will be cut, scored, or folded, you have an additional problem. UV varnish is harder than paper after curing. This means it can crack or crumble at folds during scoring.

The rule is simple - UV varnish should end minimum 2–3 mm before the scoring line. If you make varnish "overlap" the fold line, an ugly white scratch will appear during folding where the varnish chips off. I've seen business cards where the logo crossed the scoring - after folding they looked broken.

Step by Step - How to Prepare a Mask in Practice

Theory is one thing, but how do you specifically prepare a file? I'll show using the example of an A5 flyer with a logo that should be UV varnished.

You have finished graphics in InDesign - the logo is black (100% K), background is white. You want the logo to be UV varnished. First step - don't copy the logo to a separate file. Stay in the same document.

In InDesign, create a new layer and name it "UV VARNISH" or "SPOT UV". On this layer, recreate the shapes that should be varnished. Use rectangle, ellipse, or pen tool - but don't copy and paste from the original graphics. Why? Because original objects may have shadows, gradients, or effects that can't be transferred to UV varnish.

Next step - set the color. Create a new spot color named "UV" and give it the value C=0 M=0 Y=0 K=100. This is very important - it must be a spot color, not process color. In the Swatches panel, check "Spot" instead of "Process" when creating the color.

Now assign this color to all elements on the varnish layer. And here's the most important part - in the Attributes panel, enable "Overprint Fill" for all varnished objects. Without this, varnish will "knock out" white holes in the main graphics.

Final step - PDF export. Use PDF/X-1a or PDF/X-3 settings, but check that spot colors are preserved. In the export window, in the "Output" tab, set "Color Conversion" to "No Color Conversion" and disable "Include Destination Profile". UV varnish doesn't need color profiles.

Alternative Method - Separate Mask File

Some print shops prefer to receive the mask as a separate single-color PDF. In this case, create a new InDesign document with the same dimensions as the main project. Recreate on it only those elements that should be varnished - everything in black 100% K.

Save as PDF 1.3 or 1.4 without color profiles. Name the file so it's clear it's a mask - e.g., "flyer_A5_UV_MASK.pdf" or "flyer_A5_VARNISH.pdf". Always consult with the print shop which method they prefer.

Special Effects - What You Can Do with UV Varnish

UV varnish is not just a glossy logo. Once you master the basics, you can experiment with more advanced effects. Some of them can really surprise the recipient.

First effect - matte plus gloss. Instead of printing on glossy paper, use matte and apply UV varnish only to selected elements. The contrast between matte background and glossy accents is spectacular. The logo literally "pops" from the surface.

Second effect - varnish on black background. On dark colors, UV varnish gives a "wet" gloss effect, like a lacquered black car. It looks particularly effective on dark photographs - varnish can emphasize selected details, light reflections, or object contours.

Third effect - varnish without print. You can print transparent UV varnish on raw paper, without any ink underneath. On white paper it will be barely visible, but under appropriate light it becomes visible as a delicate gloss. This is a "watermark" effect - discreet but elegant.

Patterns and Textures

UV varnish can create not only flat surfaces. Depending on the print shop's technology, you can achieve textures - delicate patterns, lines, dots, or grids. This requires special screen printing formes, but the effect can be surprising.

Some print shops also offer UV varnish of different thicknesses - from very thin (satin effect) to thick (3D effect). Thicker varnish can give the impression of embossing, though it doesn't match true embossing.

Common Mistakes and How to Avoid Them

After years of working with UV varnish, I've probably seen all possible mistakes. Most of them could have been avoided if the designer or client knew a few basic rules.

Mistake number one - elements too small. The designer prepares a logo with delicate lines 0.5 points thick and wonders why the varnish looks like "smearing". Physics is relentless - thin elements won't look like they do on screen.

Mistake number two - colored mask. We receive a file where the mask is blue, green, or "very dark gray". The machine doesn't understand "almost black" color. Either it's 100% K, or varnish won't apply.

Mistake number three - gradient in mask. The designer wants varnish to "lighten" toward the edges. This is impossible - UV varnish has no halftones. At most, you can make varnish with different layer thickness, but that's completely different technology and costs much more.

Mistake number four - no overprint. The file looks great on screen, but after printing, varnish "knocks out" white holes in the background. Classic - the designer forgot to enable overprint for the varnish spot color.

Costs and Profitability of UV Varnish

Selective UV varnish is not a cheap addition, but it can be profitable with larger runs. The cost consists of preparing the screen printing forme and the varnish application itself. The forme is a one-time cost - it remains for reprints.

For small runs (500–1000 pieces), UV varnish can double the printing cost. For large runs (5000+ pieces), the addition can be 20–30%. It's worth calculating whether this effect is worth the additional cost - sometimes it's better to spend that money on better paper or other finishing.

Also remember production time. UV varnish is an additional process that extends production by 1–2 working days. If you have a very tight deadline, UV varnish may not be the best choice.

UV varnish screen printing offset spot color overprint UV mask

Selective UV varnish is a powerful tool in a designer's hands, but requires understanding technical limitations. Well-prepared varnish can transform an ordinary flyer into a premium product that the client will want to keep. Poorly prepared can ruin the best design.

The key to success is cooperation with the print shop at the design stage. Not all print shops have the same technical capabilities - some handle more delicate details better, others are better with larger surfaces. It's worth asking about limits before starting work.

If you have a specific UV varnish project to implement, don't hesitate to consult technical details. It's better to clarify doubts before printing than to correct mistakes after the fact. Ask for a quote →