How to cut glass to fit a picture frame
There’s no two ways about it, cutting glass by hand can be intimidating. Even for those with some experience, the risk of breakage still exists, and buying new glass isn’t always the cheapest thing. This tutorial probably won’t remove the overall fear of cutting glass by hand, but it will give you a number of handy pointers. That way, if you do accidentally smash a piece – it’s bound to happen the first time – you’ll know where you’re going wrong and feel more confident about not repeating that mistake when you try again.
Here at Picture Frame Studio, we send all our frames out with acrylic in (because it won’t break if the frame does happen to fall off the wall or get knocked), but in the future you may wish to replace this with glass. Particularly if you’re exhibiting in a gallery.
Step 1: Measuring-up
Your glass will need to fit inside your frame’s rebate without being too tight, but it’ll also need to fit without being too loose! Too-tight glass is hard to get in and may smash or crack if you force it, while too-loose glass is problematic for other reasons: it let’s tiny black flies in in summer and it moves around and could possibly fall out at one edge. To avoid this, ensure that the glass is around 3mm smaller than the inner size of the frame’s rebates (which is also probably the same size as your art-work or photo). Test it out before-hand with a piece of card – making sure it sits perfectly flush – and you should have a good template for the right size glass you need.
Step 2: Get a good quality glass cutting tool and some glass to practice on
Fortunately, glass cutting is a fairly specialist thing, meaning that the tools you can buy for it are generally of an acceptable, affordable standard. Look for one with either a sturdy tungsten carbide wheel, or one which requires oiling (both are ideal for cutting glass, and some of you may be familiar with these tools already: they can also be used to cut tiles to size). Otherwise, you ideally want a tool which is easy to hold and comfortable to apply pressure with. Think of it as if you would when choosing a pen and you’ll be on the right lines.
As for the glass, you ideally want a piece which is at least A4 size or bigger. Why? Because cutting a small piece of glass in two takes more skill and discipline (there’s less area to hold the glass down to the table, and also less to snap off).
Step 3: other things you will need
Now you have a tool and some glass, you’ll want to find a table to cut it on. This is also where you’ll break the glass (hopefully in the right way!).
Next up, you may want a cloth or towel to lay the glass on. Some people prefer to cut glass directly on a hard surface. The reasoning behind this is sound: in this case there will be less give between the glass and the table, meaning that there’s less chance of the glass cracking when you cut it.
Firstly, wipe any grit, dust or wood chippings off the table. Then lay your glass down, either on the table or on the towel/cloth you’ve first put on it. The next stage is to measure at the top and bottom and mark however far in you would like to cut your glass. Do this with a black marker pen. You’ll then need a ruler to lay onto the glass (a long metal ruler carrying some weight is best, and it’s even better if the under-side is felted, enabling it to stick to the glass without scratching it). It is possible to cut glass without a ruler, if you absolutely have to, but we wouldn’t advise it. You’re looking to get a nice straight line, after all.
Step 4: scoring the glass…
Scoring glass can be an unnerving experience. But in reality, providing you do it with confidence, you’re probably going to be alright.
Take your long metal ruler and line it up with your top and bottom marks. Now pick up the glass cutting tool and hold it as if you would to write. The next part is important: make sure you’re holding the tool the right way up! You want to contact the glass where the wheel protrudes more from the device.
Start at the very top, rolling the wheel slightly over the top edge before you begin to apply pressure. Then push down until you feel the wheel bite slightly into the glass. Be careful not to press too hard…unfortunately, this is simply something that comes with practice!
Now you’re ready to cut the glass. We say cut, but in fact we really mean score the glass. Cutting glass is more like scoring a piece of cardboard or leather that you’d like to fold, so don’t try and cut all the way through with the wheel (it’s a sure way to smash it!).
With the same pressure applied, pull the tool slowly towards you, running its side along the flat vertical edge of the ruler. You should hear a clean, crisp sound as this happens. You could liken it to ice breaking.
When you get to the very bottom, roll over the bottom edge and remove the ruler. Pulling the ruler away, you should see that there’s a faint but discernible white score line in the glass. Turn it over and you’ll see that it doesn’t go all the way through. You won’t be able to feel it from the other side, but don’t panic, you’ve likely done good.
Step 5: snapping the glass off
If you stand and watch a professional picture framer who’s been cutting glass half his or her life, you’ll probably be standing there thinking That looks difficult and a bit dangerous! That’s because snapping glass off takes confidence and technique. If the technique is wrong, the glass will snap, and if you don’t follow through with enough force to break the glass cleanly, you guessed it…it’ll be time to start again!
Lay the glass at the edge of a table or clean hard surface. This might be the desk where you scored the glass, or it could be somewhere else. The main thing is that you want a surface which has a solid edge.
Now put the glass half on the edge, so that the scored line you cut matches up with the exact edge of the table/desk.Happy? Then it’s time to put your left hand (if you’re left-handed, that is) on the glass on the table, and hold the glass you want to snap off in your right hand. If you’re unsure, you could use gloves, but be aware that gloves dull the senses and make it more difficult to know how much force to apply.
With your weight above the scored line, and your body to the left of the glass, push down once with a good hard action, allowing your body-weight to drive the motion. Hopefully, your glass snapped-off cleanly, leaving behind a perfect edge.
Step 6: what to do if you have a jagged edge left over
You usually get a jagged/imperfect edge when you don’t fully commit to snapping the glass. If this happens, it’s not necessarily the end of the world. With some care and attention and a good pair of metal pliers, it is possible to grab the individual jagged pieces and snap them off the glass one at a time (holding the glass on the table with one hand, as you did before). It’s not always the best solution, but if you’re fast running out of glass, it could be good enough to get the glass inside the frame.