Colorants
Colour.
One portion of additive colours 220 lbs of batch. Everything else on this page is how to get it into the glass without wrecking the melt.
One number
runs everything.
Every Glasma colour additive is sold as a single portion, and every portion is formulated for the same amount of batch: 100 kg. That is 220 lbs. What changes from colour to colour is not how much batch it treats, it is how much material is in the bag.
Colouring less than 220 lbs? Divide by weight, not by bags. Weight is the thing that scales. Work out what fraction of 220 lbs you are actually colouring, and use that same fraction of the additive. Colouring one 44 lb bag of 700 is one fifth of a portion, so weigh out one fifth of the additive. Colouring 50 lbs is 50 ÷ 220, so about 23 percent of the bag.
50 grams to 13,220 grams
Grey brown 2344 is 50 g per portion, a pinch in a small plastic bag. Black 5001 is 13,220 g per portion, and arrives in a bucket. That is a 264-fold spread across the same product line, treating the exact same 220 lbs of batch.
So there is no rule of thumb, no scoop, no handful. Every colour has its own number, it is printed on that colour's product page, and it is in the chart at the bottom of this page. Look it up every time.
Weight is not a proxy for how dark it reads
A heavy portion does not mean a dark glass. Yellow 2345 needs 12,350 g and is not a dark colour at all. Grey dark 2900 gets there on 460 g. The weight reflects how much material that particular chemistry needs to develop, nothing more.
Sprinkle it on
the charge.
There are two ways to do this. You can premix the additive into the pellets in a drum or a mixer before charging, or you can sprinkle it straight onto the batch as it goes into the furnace. Both work. We recommend sprinkling it onto the charge, and the reason is not melt quality, it is handling.
Premixing means a drum, a mixer, scoops and a floor that all now have colourant on them. Every one of those is something you have to clean before the next colour, and every one of them is a chance to contaminate a later melt or a bag of clear. Sprinkling on the charge skips all of it. For the small-weight colours it is genuinely trivial. For the heavy ones like yellow, black or the ambers it takes more care, but it is still simpler than decontaminating equipment.
Weigh the portion out first
Work out how much batch this charge cycle will use, scale the additive to it by weight, and weigh it before you start charging. Do not do this math with a hot furnace open in front of you.
A cheap digital kitchen scale covers the light colours. The heavy ones you can weigh on a shipping scale.
Split it across your charges
You are not filling the furnace in one go, so do not add the colour in one go either. Divide the additive roughly in proportion to the charges. If you are building the melt in five charges, put about a fifth of the additive on each.
Spread it across the surface of the mound rather than dumping it in one spot.
Let the melt do the mixing
Pelletized batch releases gas at several stages as it melts, and that movement carries the colour through. This is Glasma's own point about why pellets distribute additive better than a traditional sand batch would.
Follow the normal melting method from there: charge to full, hold hot until the bubbles stop changing, then drop the temperature for the squeeze.
Full method: the Melting & Annealing guide
If the colour comes out uneven, premix next time
Streaks, blotches or a colour that shifts between gathers means the additive did not distribute. That is the signal to premix rather than sprinkle.
To premix: tumble the pellets and additive together in a lidded steel drum rolled on the floor, or run a cement mixer that has never held concrete. A light mist of water helps the additive cling to the pellets instead of sifting to the bottom. Keep a dedicated drum per colour and you avoid most of the cleaning problem.
Do not throw a sealed bag of additive into the pot
It has been tried. The bag burns off and leaves the colourant in one concentrated lump, which rarely distributes evenly, and the burning plastic can introduce flaws of its own. Glasma does not recommend it and neither do we. Sprinkling loose additive across the surface of a charge is a different thing entirely, and that is what we are describing above.
You can go lighter.
Going heavier breaks things.
Want a paler version of a colour? Use less. Half the additive gives you roughly half the density and nothing bad happens to the glass. That direction is safe, and it is the cheapest experiment in the shop.
Going the other way is where people get hurt. These additives are engineered against a specific ratio, and pushing past it does not simply give you more colour. It changes the glass.
What over-dosing actually does
Per Glasma: you get different melting behaviour, a change in viscosity that often leaves the glass very runny and short, a shifted coefficient of expansion that at some point makes the colour impossible to combine with clear without cracking, changed annealing requirements, and frequently a different colour tone than the one you were chasing.
That last one surprises people. Push a colour hard enough and you do not get an intense version of it, you get a different colour.
"I was pushing the concentration of the chemicals quite a bit. I wished a bit denser colour for some of the designs I am working on. After the failure I carefully broke up and mixed the lumps that had formed in the 2345. I made a new mix in the recommended ratio and all looks good."
That melt came out brown instead of yellow, and runny enough to be difficult to work. At spec, the same additive was fine.
There is a ceiling, and it is not Kugler
The Glasma colour system is transparent colour built on a clear studio batch. It is not designed to reach the density of a dedicated colour bar from Kugler or Reichenbach, and there is no dense white opal additive in the line. Reaching that kind of saturation would require reformulating the base batch, not adding more colourant to this one.
Melt temperature
does not change COE.
Colour does.
This comes up constantly, so plainly: running your melt at 2150°F instead of 2350°F does not change the coefficient of expansion of the finished glass. Temperature changes how the melt behaves, how fast it clears and how it works on the pipe. It does not rewrite the chemistry.
Adding colourant does change it. Every gram of additive is a change to the glass composition, and COE moves with composition. At normal dosing the shift is small and colours combine with clear the way you would expect. The more additive you add, the further it drifts, and past some point a heavily coloured glass will not sit next to clear without cracking.
Dose it at spec and compatibility is a non-issue
The published tolerance on the base batch is COE 98 ±2, and Glasma is fine-tuning that downward for closer compatibility with the major colour makers. A common rule of thumb in the trade is that a mismatch within about ±5 COE will not usually cause problems.
So the risk is not colour in general, it is heavy colour. If you are dosing at or below the recommended portion, this is not something you need to worry about. If you have been pushing the ratio, it is one of the first things to suspect when work starts cracking.
Colour wants
fresh batch.
The portions are formulated against 100 kg of fresh pelletized batch, and that is the melt they are designed for. Pellets are loose, they are still breaking down as they go, and the additive gets carried into the glass by the whole batch turning over. Melting colour on fresh batch is best practice, and it is what we would tell you to do every time.
Where we part ways with the Glasma guide
Glasma's colour system guide indicates the additives can be used with cullet. We are not going to tell you that flatly. Some colours will take in cullet. Others will streak, and you will be stirring a lot harder than you expected to get an even result.
The reason is mechanical, not chemical. A charge of cullet is solid glass sitting in a heap. Powder dropped onto it tends to sit on the surface or work into the gaps rather than distribute, and once the cullet goes plastic you are relying entirely on convection and your own stirring to move the colour through a body of glass that is already formed. Fresh batch does that work for you.
If you are going to do it anyway
Use the lighter portions rather than the heavy ones, plan on stirring or plunging and then giving it a long soak, and expect the shade to land somewhere other than where the same portion lands on fresh batch. Pull a test gather before you commit a day's work to it.
None of this is an argument against cullet. Cullet is good economics and it melts fast, and the melting guide makes the case for charging your own clean returns with your batch. Colour is the exception to that, not a contradiction of it. Melt your cullet clear and put your colour on fresh batch.
Stir it.
The old way
still works.
Sprinkling the additive on the charge gets it into the furnace. It does not guarantee it ends up evenly distributed through the whole body of glass. Convection does most of that work on a fresh batch melt, but we recommend stirring, and we recommend it strongly if you are running a heavy colour, a deep pot, or anything with cullet in it.
You do not need equipment for this. The traditional method is a raw potato on the end of a punty, plunged into the melt.
Skewer a raw potato on a punty
A whole raw potato, pushed firmly onto the end of a cold punty so it will not slide off. Green apples and a green stick of hardwood do the same job. What matters is that it is wet and organic.
Use a punty you do not care about. It is going to take a beating.
Plunge it into the melt and hold
Push it below the surface and keep it there. The water in the potato flashes to steam instantly and the whole mass of glass begins to boil and churn. That churning is the stir. It is moving glass from the bottom of the pot to the top in a way no paddle is going to match.
Work it slowly around the pot rather than holding it in one place. You want the turnover happening everywhere, not just in one column.
Let it settle before you judge the colour
You have just filled the glass with bubbles on purpose. Bring the melt back up, hold it hot and let it fine out before you decide whether the colour is even. Judging a freshly plunged melt tells you nothing.
Fining and annealing method: the Melting & Annealing guide
The big bubbles do double duty
The large bubbles a plunge creates rise fast, and on the way up they sweep smaller bubbles along with them. So a plunge is both a stir and a fining aid. This is why the technique survived as long as it has, and it is worth knowing even when you are melting clear.
This is a steam event, treat it like one
Plunging water into molten glass produces a violent, immediate reaction. Face shield, long sleeves, gloves, and nobody standing beside you. Go in at arm's length and go in deliberately rather than dropping it. Never plunge something soaking wet or sealed, and never plunge into a pot that is already full to the lip, because the melt will rise and you want somewhere for it to go.
If plunging is not something you want to do, a graphite or steel paddle worked slowly through the melt will also move colour around, and so will a long soak at temperature. They are slower and less thorough. The potato is cheap, and it is what we would reach for.
Light to dark.
Then be honest
about the pot.
If you are running more than one colour through the same pot, always work from the weakest colour toward the strongest. Whatever is left behind from the previous melt gets diluted into something stronger, where it matters least. Go the other way and a trace of black will haunt every light colour that follows.
That is the easy part. The hard part is what nobody can tell you: how much clear it takes to flush a colour out. It depends on your furnace, your pot, how deep the colour was and how much of it soaked into the refractory. There is no published number because there is no honest one.
Some colours may never fully wash out
Light and mid-tone colours will dilute away with enough clear. The deep blues and the black are a different matter, and we would not promise you that a pot which has held black will ever return to clean clear.
We worked light to dark through the range in a small furnace here a few years ago, and we trashed the pot at the end. That was the plan going in. If you are not willing to do that, do not put your darkest colours through the pot you rely on for clear.
If colour is going to be a regular part of what you make rather than an occasional experiment, the answer is a dedicated colour pot, or a small second furnace. Melting 400 lbs of colour in the furnace you need for clear tomorrow is how studios end up with an expensive problem.
Colours don't all
work the same.
A coloured melt is a different material from your clear, and the difference shows up at the bench. Expect the working temperature that suits one colour to be wrong for another, sometimes by a lot.
"The Glasma colours varied greatly in viscosity. I work [my clear] at 2180[°F] measured between the elements and the crucible. At that temp the yellow was like water, the turquoise slightly more viscous than [my clear] and the green we had to cut off the tails after a gather. If I had my choice I would work the yellow at 2050, turquoise at 2190 and the green at 2210."
Plan to find your own number for each colour. Start where you normally work, take a gather, and adjust. A colour that pulls long tails wants more heat. One that runs like water wants less.
Seeds appearing as the day goes on usually means too hot
If a colour starts clean and gets seedier over the course of a session, the most likely cause is that you are holding it hot enough to boil the glass. Drop the temperature and the seeds generally go back in. This is the same squeeze behaviour described in the melting guide, and it applies to colour exactly as it does to clear.
Shade varies, and that is normal
Glasma is explicit that colour shade may vary from furnace to furnace and even from batch to batch. Atmosphere, temperature, how long it sat hot and what the pot has seen all move the result. A shade that does not exactly match your last melt is not usually a defect in the additive or the batch.
Treat the powder
with respect.
The additives are concentrated metal oxide compounds. In the glass they are inert. Loose in the air of your shop they are not, and this is the part of colour work that is easiest to get casual about.
Do not raise dust
Pour low and slow, avoid shaking or dropping the bag, and do not let a fan or the furnace draft catch loose powder. Inhalation is the exposure route that matters here. Ventilation and a respirator are reasonable precautions when you are handling the heavier portions.
Sweep or vacuum residue, do not wash it away
Some additive will end up in your scoop, your chute or on the floor no matter how carefully you work. Collect it dry. It does not belong in a drain, and it does not belong in the regular trash either. In Europe this waste is legally classified as hazardous, and while your local rules may differ, the substance does not.
Save the remnants for a final melt
The practical solution most studios land on is to collect colourant residue over time in a sealed container, then melt all of it into one last dark melt before a pot change. The colour goes into glass instead of into a waste stream, and the pot was coming out anyway.
Read the SDS for the colour you are using
Every additive has its own safety data sheet with the specific hazards for that chemistry, and they are not interchangeable. Every one of them is linked from the chart below. The base batch has its own sheets too: Glasma 700A and Glasma 725A. These are issued by Glasma AB under EU regulation, so the emergency numbers and exposure limits cited are European.
All 25 colours,
and what one
portion weighs.
Every weight below is the full portion for 220 lbs of batch. Grouped by family, and within each family sorted from the lightest portion to the heaviest. Current price and stock live on each product page, and the safety data sheet for every colour is linked in the last column.
Greys
| Colour | Code | Per 220 lbs | SDS |
|---|---|---|---|
| Grey brown | 2344 | 50 g | |
| Grey light | 2554 | 70 g | |
| Grey | 5009 | 230 g | |
| Grey dark | 2900 | 460 g |
Blues & Turquoise
| Colour | Code | Per 220 lbs | SDS |
|---|---|---|---|
| Turquoise light | 2555 | 270 g | |
| Blue light | 2428 | 280 g | |
| Turquoise green | 2461 | 300 g | |
| Blue turquoise | 2430 | 500 g | |
| Blue dark | 2295 | 760 g | |
| Turquoise blue | 2871 | 770 g | |
| Turquoise dark | 2433 | 1,520 g |
Greens
| Colour | Code | Per 220 lbs | SDS |
|---|---|---|---|
| Green dark | 2298 | 760 g | |
| Green light | 2463 | 1,350 g | |
| Green turquoise | 2305 | 1,550 g | |
| Green olive | 2666 | 1,790 g | |
| Yellow green | 2466 | 2,400 g | |
| Green lime | 2873 | 12,410 g |
Pinks & Lilacs
| Colour | Code | Per 220 lbs | SDS |
|---|---|---|---|
| Pink lilac | 2559 | 2,960 g | |
| Blue lilac | 2561 | 2,960 g | |
| Lilac blue | 2562 | 2,960 g | |
| Pink | 5005 | 4,990 g |
Ambers & Yellow
| Colour | Code | Per 220 lbs | SDS |
|---|---|---|---|
| Amber dark | 5002 | 8,450 g | |
| Yellow | 2345 | 12,350 g | |
| Amber light | 2475 | 12,900 g |
Black
| Colour | Code | Per 220 lbs | SDS |
|---|---|---|---|
| Black (dark blue) | 5001 | 13,220 g |
Note that 2559 Pink lilac, 2561 Blue lilac and 2562 Lilac blue are all dosed at 2,960 g. They are genuinely different colours, and 2559 in particular shifts between blue and lilac depending on the light it is viewed in.
Shop the colour additives
Live price and stock on every colour. Colours ship separately from batch and are ordered the same way, on the site.
Get the clear melt
right first.
Colour multiplies whatever your melt is already doing. If you are still fighting bubbles or cords in clear, sort that out before you spend money on additive, because a colour melt will not be more forgiving.
Melting & Annealing
The method we teach on the phone: charge to full, hold hot until the bubbles stop changing, then drop the temp for the squeeze. Plus the annealing math.
Cords
Streaks of off-composition glass, and why they are a mixing problem rather than a heat problem. Directly relevant if your colour is coming out streaky.
First colour melt?
Tell us which colour and how much batch you are treating, and we will check your math before you open the bag.
Email us your colour question