I love decorating pots with floral patterns outlined in sharp black line art. I used to spend hours unclogging trailing tips, stretching sore hands, and worrying about whether this line would be the one where I squeezed too hard and underglaze splattered everywhere. A year ago, some new tips, a few new tools, and a bit of experimentation made me realize something wonderful (and a little bit crazy)—trailing underglaze lines can be rhythmic and soothing, rather than time consuming and stressful.

Underglaze Trailing Materials

  • Fineline Precision Applicator Tube with 18- and 20-mm gauge tips included
  • Underglazes: I use a variety of Amaco Velvet underglazes
  • Water for dilution
  • Funnel

The Fineline Precision Applicator Tubes have three main advantages that have made them my go-to tool when decorating. First, the shape reduces fatigue. The tube feels like holding a marker, which is more familiar to my hands than thicker or flat bottles.

Second, the tube is flexible. The plastic body is thin and easy to squeeze, requiring less pressure, and therefore reducing hand and arm fatigue.

Third, the integrated pin caps prevent drying, solve clogging, and aren’t easily lost. The caps for these tips have a dull pin attached to the inside that seals the applicator when not in use and can be used to unclog your tip. They’re also much easier to locate than a loose sewing pin!

1 Using a funnel, pour in underglaze, and use a paintbrush to push it through.2 Continue to fill until just a centimeter shy of being full. Fill the rest with water.


Filling the Tube

To prepare an applicator full of underglaze for line art, fill the tube with Amaco Velvet Jet Black underglaze using a funnel. Use a paintbrush to push it through the neck of the funnel if this proves difficult (1). Continue until the tube is a centimeter shy of being full. Add water to the underglaze until you fill the rest of the tube (2). Screw the cap back on and shake it until the underglaze is evenly diluted and resembles the consistency of ketchup: smooth and thin, but moving as one unit. If necessary, I add a couple drops of water at a time, place the cap back on, then shake the tube (3), before testing the consistency on the back of my hand. The underglaze should squeeze out easily without much pressure, leave a slightly raised line, and not bleed into the crevices of your skin.

I recommend practicing on a scrap piece of bone-dry clay (4), getting a feel for how hard to squeeze the applicator, how to hold it, and what motions come most naturally. I hold my applicator as I do a pencil, but move with my wrist and arm for quick, smooth, and sweeping gestures. Adjusting the pot itself, or your entire body, can eliminate the need to make movements that feel unnatural, and subsequently lead to skewed or shaky lines.

3 Screw the cap back on and shake until the underglaze is evenly diluted.4 Practice drawing thin and thick lines on a piece of bone-dry clay.


Laying the Foundation

Using a fan brush, apply white underglaze to a leather-hard cup. Attach a handle and set aside until it is fully bone dry. I apply both my colors and line art on bone-dry, unfired clay.

5 Outline your colorful design using the black underglaze-filled applicator.Next, apply 2–3 layers of colorful underglaze, laying out a floral pattern. Wait for each layer to dry before applying the next. Underglaze layers are absorbed much quicker when working on bone-dry clay, increasing my decorating pace. Because the dry surface cannot be reshaped, scraping the applicator tip into the clay when drawing line art is nearly impossible, which helps prevent clogging.

Adding the Line Art

Different tip sizes are the most reliable way to create thicker and thinner lines; an 18-mm gauge is my preferred thin line and comes out similarly to a fine point Sharpie marker, while a 20-mm gauge more closely resembles a dull pencil. These are the only two sizes made by Fineline Applicators, so for more controlled variety, you may want to consider another tool. That being said, a very thin underglaze mixture, which might be necessary for smaller tips, will bleed out and become a thicker, less opaque, and less controlled line.

Outline your design using the black underglaze-filled applicator (5). I try to be carefree during this step because when I concentrate too hard, my movements slow down and my lines become less smooth and lively. My approach is, after all, that rather than color outside the lines, I’d like to create colors and then draw my own lines.

When you’re done trailing for the day, screw your applicator caps on tightly before storing. There is no need to empty the tube. The caps’ pins will seal the tubes tight, the underglazes won’t dry out or clog the tip, and you can start using them right away the next time you decorate

6 Wildflower Mix Mug, buff stoneware, underglazes, clear glaze, 2020.

Troubleshooting Tips

Correcting an error on bone-dry clay is difficult because scraping the hard, fragile surface creates dust you shouldn’t breathe in and is also generally time consuming. Working on clay that still has moisture makes it easier to scrape off a stray line, lay down new underglaze, and retrail.

Alternatively, you could work on bisqueware, where any mistakes can be washed away with water and decorating done again once the bisqueware fully dries.

The third option (and my favorite) is to embrace the mistake, whether that means creating a second loopy layer of line art or altering your overall pattern.

Lucy Nguyen is a potter from Arlington, Virginia. She creates functional work, primarily mugs. She can be found on Instagram @lucynguyenpottery with a collection of process shots, videos, and finished work.