Converting C-41/E-6 BLIX into Separate Bleach and Fixer
Many C-41 and E-6 kits come with BLIXes to remove silver. These BLIXes sometimes don't work all that well, and some of the BLIX concentrates have limited shelf life. The main purpose of this document is to provide a brief introduction into the composition and inner working of bleaches and BLIXes. We then use this knowledge to convert BLIX concentrates and powders as provided by kit makers into separate bleaches and fixers, using only compounds that can be easily obtained by photo amateurs, and using only tools and equipment that can be found in most simple dark rooms.
I split this document into three sections: the first section will describe what bleaches, fixers and BLIXes for color work do, and how they do it. The second section will describe the chemistry and equipment needed to convert commonly available BLIX concentates or powders into separate bleach and fixer suitable for C-41 and E-6. Finally, the third chapter will describe the procedure for making the desired bathes and how to use them in the standard process chain.
2 Composition and Working Principles of Bleaches, Fixers and BLIXes for Color Work
2.1 Bleach: oxidizes silver and creates a silver salt that may or may not be water soluble. A bleach needs two main components: an oxidizer, and a compound which supplies the anion to the newly formed silver salt. The stronger the oxidizer, the more active the bleach will be. Likewise, the bleach will be stronger, the stronger that anion binds silver ions (and therefore removes them from the process). A special case of this anion is the group of anions which form tight, water soluble complexes with silver ions: these compounds are used to make BLIXes (see further down).
The whole reaction can be thought of as a push/pull reaction: the oxidizer pushes the silver towards ionization, and the anion pulls the silver ions away from the pool. Together these two reactions convert metallic silver into a silver salt. A strong bleach needs a strong oxidizer and a compound that forms a highly insoluble salt. Note, that bleach strength depends not only on the kind of compounds used, but also on their concentration, with higher concentrations generally yielding stronger bleach.
There are a few compounds commonly used for bleaching silver:
- Ferricyanide: very powerful oxidizer for silver. Although many home brewers use them successfully for E6 and C41, these two processes are neither specified nor tested for Ferricyanide bleach and YMMV. Since stable BLIXes can not be made from Ferricyanide, these compounds won't be of significance for the rest of the document.
- Ferric PDTA bleaches are also quite powerful, and come with several professional C41 kits. These bleaches are not officially blessed by the manufacturers for E6 work. Since stable BLIXes can not be made from Ferric PDTA, these compounds won't be of significance for the rest of the document.
- Ferric EDTA bleaches/BLIXes use the weakest bleach compound, and the only one of the three that can be used to make a somewhat stable BLIX. It works well for C41 and E6, and most kits use this compound. This is what we expect to find in one of the liquid BLIX concentrates, whereas with powder kits that usually come with Sodium Ferric EDTA (see further down). Ferric EDTA containing liquids are easily recognizable by their very strong, saturated, dark red (almost black) color.
By far the most common compound which supplies the anion to the silver ion is Bromide: usually supplied as Ammonium/Sodium/Potassium Bromide. It binds silver ions less effectively as Iodide (solubility of AgI is orders of magnitude below that of AgBr), but the resulting AgBr is moderately easy to remove in the fixing stage, very much unlike AgI. Another advantage of Bromide over Iodide is its stability in aqueous solution: Iodide will be converted to mostly inactive (for the purpose) Iodate by aerial oxygen over time, and the oxidizer already present in the bleach certainly won't help here either.
C-41 bleaches will consist of either Ammonium Ferric PDTA or Ammonium Ferric EDTA, and some source of Bromide. Bleaches for E-6 have to use the weaker Ammonium Ferric EDTA together with Bromide.
2.2 Fixer: removes the insoluble silver salts created by the bleach or left behind by previous development steps. Since fixer (or BLIX) is the last concentrated liquid in touch with the film strips, fixer pH is critical: Dyes are chemical compounds which absorb a range of wavelengths. This range depends on the degree of ionization, and therefore on the pH of the final bath. This variation in hue may be subtle, but it is there. The dyes used for C-41 and E-6 products are formulated in such a way that they have their correct hue at pH 6.5.
2.3 BLIX: is a special variant of bleach, where the anion provided forms a water soluble compound with silver ions. As a result, only one bath is needed to completely remove all metallic silver (and silver ions) from the emulsion. While this sounds like a great improvement, it comes at a price:
- bleach works optimally at low pH (4 - 5.5), but dyes require pH 6.5 in final bath. This means a correctly formulated BLIX will have weak bleaching action.
- the bleaching compound used in BLIXes will slowly oxidize the fixer (usually Thiosulfate), therefore shelf life of BLIXes is short.
- Ferric EDTA is a rather weak oxidizer for silver, so it must be present in high concentration. At the same time fixers become much weaker if high concentrations of other compounds are present. Therefore there is a limit to the strength of a BLIX, which may or may not be sufficient for complete silver removal.
- fixer compound is cheap, but bleach compound is expensive. Since used fixer becomes weaker with use, a BLIX can not be reused very often. There is already a weakened bleach component (too high pH), together with a weak silver ion scavenger (used Thiosulfate) a BLIX will become ineffective very quickly. You have to throw out the whole thing (bleach component and fixer), just because the fixer became weak (remember push/pull).
Since alleged ease of use often trumps quality results, most amateur color processing kits come with BLIXes. Fortunately for us, most vendors supply the BLIX as two components, of which one is mostly oxidizer, and the other one is mostly fixer. It is therefore possible to make a separate bleach from one concentrate or powder (together with other compounds) and discard the other one.
3 Required Equipment and Materials:
3.1 Tools: there will be some weighing and mixing involved, so we need:
- Beakers for the amount of liquid we want to mix
- Scales that are at least accurate down to 1 gram. These are easily available and very cheap.
- Spatulas or spoons dedicated to chemical use
- A flat surface for doing the measuring and mixing
Most of these may already be present in a decently equipped dark room, but the scales and the spoons/spatulas may have to be purchased for this purpose.
3.2 Chemistry: depending on which BLIX kit we start with, different compounds will be needed. Some can be sourced either from well stocked pharmacies or hardware stores, or (depending on region) from Formulary or Suvatlar.
The following items may end up on your shopping list:
- Ammonium or Potassium Bromide
- Sodium Bicarbonate (you won't need this if you have a pH meter)
- 20-80% Acetic Acid
- a neutral rapid fixer at pH 6.5
There are several commercial products for neutral rapid fixer, most notably Formulary's TF-5 and Tetenal's Superfix Odourless. I'm sure there are more. If you feel like self mixing, there is Ryuji Suzuki's neutral rapid fixer and Ron Mowrey's superfix.
4.1 Identifying the Kit and its Constituents
First of all, let's take a look at what you have. People with powder kits (Unicolor, Tetenal) seem to get Sodium Ferric EDTA plus extra stuff in one of their two BLIX parts, whereas liquid kits (Tetenal, Arista) provide Ammonium Ferric EDTA. You need to figure out which BLIX part contains the Ferric EDTA, and which form of Ferric EDTA you have.
Here are some pointers:
- Tetenal Colortec C-41 and E-6: Ammonium Ferric EDTA is provided in the bottle labeled "BX1".
- Arista C-41 Liquid Color Negative Developing Kit: Ammonium Ferric EDTA is provided in the bottle labeled "BLIX PART B"
- Tetenal C-41 Press Kit for Color Negative Film and Unicolor Powder C-41 Film Negative Processing Kit: Sodium Ferric EDTA is supplied in the bag labelled "POWDER BLIX B"
- Rollei/Digibase/Fuji C-41 kits: these kits already provide separate bleach and fixer, there is no need for further action.
I would welcome additions in the comments section!
I recommend against using the fixer component of your BLIX kit for the following reasons:
- it comes with extra stuff which makes it a weak fixer
- you need to reach pH 6.5 +/- 0.1, which is impossible withˇut a pH meter
- it's the liquid BLIX part containing the fixer component which most often goes bad first.
- the bleach will outlast the fixer component many times over, so you need more fixer anyway before you replace the bleach.
Neutral rapid fixers have excellent shelf life (much longer than their acidic breethens), and you can fix at least 6 rolls of film (135 or 120) with one 500ml batch of neutral rapid fixer.
4.2 Mixing the Bleach
If the kit comes with Sodium Ferric EDTA (see above), you need to add Ammonium Bromide to make your bleach more active. With Ammonium Ferric EDTA you can choose between Ammonium, Sodium and Potassium Bromide, with the latter ones likely cheaper and more convenient in handling.
If you have a powder kit, you have to mix the whole thing at once, whereas liquid kits allow partial mixing. I will now provide instructions for mixing 1000ml of bleach, because that is the most commonly mixed amount. Mixing instructions for 250ml or 500ml are similar in procedure with linearly scaled amounts.
For 1000ml bleach you need:
- the powder or liquid from your kit that contains the Ferric EDTA (see above)
- 50 - 100 g Bromide (see above). More Bromide makes the bleach last longer (more film rolls per batch, not shelf life)
- water to make 900 ml
That bleach as is may or may not be active, quite likely its pH will be too high. If you have a pH meter, adjust the bleach to pH 5.5 with Acetic Acid and be done with it. People who don't have a pH meter can use the following procedure to get pH into the right ball park and thereby obtain a working bleach:
- Add 10 ml Acetic Acid 80% (or 25 ml Acetic Acid 30%) to your 1000 ml batch of bleach, stir well
- Take 10 ml (or 25 ml if you added Acetic Acid 30%) of this new bleach into a small beaker, and drip in some baking soda.
- If it fizzles and bubbles, you are done, otherwise proceed with step 1.
With or without pH meter, don't forget to fill up to 1000ml with water before you use the bleach!
Shelf life of this bleach is at least a few months, and you can successfully bleach at least a dozen of rolls (135 and 120) in that time frame.
4.3 Bleach and Fix Procedure
The normal C-41 routine is color developer, BLIX, wash, STAB, although frequently appearing problems (yellow streaks in blue regions) suggest that the routine should be color developer, stop, wash, BLIX, wash, STAB. With separate bleach and fixer this routine morphs into color developer, stop, wash, bleach, wash, fix, wash, STAB. This means the BLIX step is converted into a bleach, wash, fix sequence with no other changes done to the process.
Likewise with E-6, the typically suggested routine first developer, wash, color developer, wash, BLIX, wash, STAB morphs into the sequence first developer, wash, color developer, wash, bleach, wash, fxi, wash, STAB. Again, the BLIX step is converted into a bleach, wash, fix sequence with no other changes done to the process.
You have a working bleach and fixer, now let's put them to use: by the time your film strips need bleaching, have the bleach ready at 38░C/100░F and use it for 7-10 minutes with the typical amount of agitation. After pouring out the bleach, wash thoroughly for 3-4 minutes, ideally with warm water. After that wash, have neutral rapid fixer ready at 38░C/100░F and fix for 3-5 minutes. Wash film thoroughly, then immerse in STAB as prescribed by your kit's instructions. If your kit doesn't have a STAB, get a separate bottle with STAB from another vendor or mix your own.
Trying to be the best of whatever I am, even if what I am is no good.
A quick update regarding identification whether a kit is bleach&fix vs. BLIX: There is a kit sold in the US under the "Rollei" brand which is a liquid BLIX kit, unlike the Rollei Digibase kits sold in Europe. To add to the confusion, there was a kit sold in the US under the Rollei Compard brand, which provided separate bleach and fixer.
Trying to be the best of whatever I am, even if what I am is no good.
Originally Posted by Rudeofus
I noticed this last night while I was searching around for separate bleach and fix C-41 kits. It appears that the only liquid 1-5L C-41 kits with separate bleach and fix chemicals are available exclusively in Europe.
What are the visual signs of exhausted/ inadequate bleaching?