Beginner’s Blunders: Copper Foiling Errors Every New Glass Artist Makes

At Caveman Glassworks in Centerville, Texas, we meet students every week who are stepping into the magical world of stained glass for the very first time. Whether you’ve signed up for our suncatcher workshop, mosaic stepping-stone class, or are diving into a copper foil beginner project, one thing is always the same: you’re excited to learn but a little nervous about making mistakes.

And that’s okay—every stained glass artist started exactly where you are now.

Copper foiling—the step that brings all your pieces together before soldering—is one of the most common places where students stumble. The good news? Those mistakes aren’t failures—they’re lessons. In this guide, we’ll walk you through the most common beginner blunders (that we see right here in our classes!) and show you how to avoid them.

Off-Centered or Uneven Foil Application

The mistake: Beginners often apply foil that sits too far to one side, leaving one edge with lots of copper and the other barely covered.

Why it matters: Solder only sticks to foil, not bare glass. Uneven foil leads to thin solder on one side and bulky solder on the other, which makes your project look crooked under the light.

How to fix it as a student: Slow down. Lay the foil gently and keep it “floating” until you’re sure it’s centered. Only then should you press it down. If it’s way off, don’t be afraid to peel it back and try again. Even experienced artists redo pieces—fixing foil is normal!

👉 For more insights, see our post Top Five Mistakes Beginners Make With Stained Glass.

Wrinkled or Cracked Foil Around Curves

The mistake: Pulling too hard when applying foil around curves causes wrinkles, creases, or cracks.

Why it matters: Wrinkles weaken the bond, and cracks expose glass edges. When you solder, these flaws become glaring gaps or bumps.

How to avoid it:

• Use narrower foil for tight curves.

• Don’t stretch—let the foil bend naturally.

• If wrinkles appear, smooth them flat with a burnisher before moving on.

👉 Learn how the right foil choice matters in our post Choosing the Correct Copper Foil for Stained Glass.

Overlapping Tape Too Much at the Ends

The mistake: Beginners often overlap the foil ends by half an inch or more, thinking this makes it “extra secure.”

Why it matters: Thick overlaps create a bulge that solder exaggerates, making your lines uneven. The solder also doesn’t flow well over double foil.

The fix: Overlap just enough to meet—about ⅛ of an inch is all you need. Press the seam firmly so it lies flat and smooth.

👉 As our Top Five Mistakes Beginners Make article reminds students: patience always pays off in foiling and soldering.

Forgetting to Burnish (or Not Burnishing Enough)

The mistake: Some students lightly tap down the foil and call it good.

Why it matters: If foil isn’t pressed tightly, it will lift when the heat of the soldering iron hits it. That lets solder sneak underneath and create ugly bumps.

How to do it right:

• Use a fid, plastic wand, or the back of a spoon.

• Press from the middle out toward the edges.

• Smooth both sides of the glass thoroughly.

Using Old, Tarnished, or Dirty Tape

The mistake: Using foil that’s been sitting in a drawer for years, or handling tape with dusty, oily fingers.

Why it matters: Tarnished foil resists solder, and dirty tape won’t stick well. No matter how good your technique is, the final piece will look sloppy.

Best practice:

• Buy fresh foil and check that it’s shiny copper.

• Store it in a sealed bag to prevent oxidation.

• Wash your hands or wear gloves before handling.

Skipping Edge Grinding (or Grinding Too Much)

The mistake: Foiling sharp, jagged edges—or grinding so much the glass becomes rounded.

Why it matters: Foil tears on sharp edges and slips off rounded ones. Solder lines end up weak or messy.

Fix it: Grind just enough to smooth the glass. Then wash the piece to remove dust before foiling.

Waiting Too Long to Solder (Humidity Problems)

The mistake: Letting foiled pieces sit for several days (or longer) before soldering.

Why it matters: In humid conditions, adhesive weakens and foil starts peeling. By the time you solder, pieces may already be coming loose.

Solution: Try to solder within 24–48 hours of foiling. If you must wait, store projects in a sealed container with silica gel packs to absorb moisture.

Overlooking Safety Basics

The mistake: Forgetting that stained glass involves sharp tools, chemicals, and lead.

Safety reminders:

• Wear safety glasses when cutting or grinding.

• Use ventilation or a fan when soldering—flux fumes are harsh.

Wash your hands often to avoid lead exposure.

👉 As our Stained Glass Safety Gear article reminds students: Safety First and equipment to consider.

At Caveman Glassworks, we remind every student: “Every wrinkle, bubble, or crooked line is just part of the journey.” With each project, your foil lines get straighter, your solder flows smoother, and your confidence grows.

So don’t let blunders discourage you—celebrate them as stepping stones. Every stained glass artist has been there.

Quick Student Checklist for Foiling Success

Step	What to Remember
Cut & Grind	Smooth edges, don’t over-grind. Clean before foiling.
Foil Choice	Use fresh foil; right width for your project.
Apply	Center the tape, overlap slightly.
Curves	Narrower foil, don’t stretch too tight.
Burnish	Press firmly—no bubbles, no gaps.
Timing	Solder within 1–2 days if possible.
Safety	Glasses, ventilation, and clean hands.

Articles to consider reading:

Stained glass safety gear

Types of Stained Glass

Selecting Colors for My Stained Glass Project