While we at Tantec realize that tanners are expert at running leather trials, we have been asked often about details of how to run a fungicide trial.  Here are our suggestions.

The basic technique in trialling a new fungicide is very simple.  Use the new fungicide on a full sized load of hides, according to the supplier’s recommendations.  Take samples at the end and test them for mould resistance.

However, apart from these simple instructions, here are some extra points worth noting.

The Trial

1. It is best to run your trial in a full size processor, with a full size load.  This is because trial drums are not quite the same in performance, and could lead to misleading results.
2. Take careful note of addition requirements.  These include the following questions, which the supplier of the fungicide should be able to answer:
1. How much fungicide is required?
2. Where to add it?
3. Is pre-dilution required?
4. Can it be added in one dose, or should it be drip fed over a longer period?
5. Are there incompatible dose points, such as close to basification?
6. How long after addition should the process run before taking samples?
3. A common mistake is to take too few samples for mould resistance testing.  Two or three sets of results may be very misleading.  At Tantec, we recommend a minimum of ten samples for each trial treatment - more if possible.
4. After taking the samples, you may then wish to add your standard fungicide at the standard dose, and run for a further hour or two, as insurance, to make sure the load is well protected against mould attack. We think this is good practice.

Taking Samples
As mentioned, we strongly recommend at least ten samples per trial treatment.  The standard size for the Tantec tropical chamber is 110 by 70 mm.  If you cut larger samples, and send them to us, we will trim them to size. We suggest you cut all samples from the same part of the hide.  Neck samples are fine. At least ten samples, one from each of ten different hides.

We recommend you take ten or more samples from a batch of normal production, as well as from trials. Once the samples are cut, each lot should be placed in a sealable plastic bag, and labeled with batch number (or other code) and NOT with the treatment.  This is to make sure there can be no bias on the part of Tantec (or anyone else) in carrying out mould resistance testing.  Keep a careful record of which batch is which, and inform the tester of this key only AFTER results are final.
 

Send samples to :
Lance Kennedy
Tantec,
48 Penzance Road,
Mairangi Bay,
Auckland,
New Zealand.

You may wish to send similar sets of samples to other organizations for parallel testing.

Mould Resistance Testing
The aim of this testing is to compare the performance of various treatments. There is no certain way to relate time that a sample remains mould-free any laboratory test, to the time wet blues remain mould free in the real world.  Any such suggestion is guesswork only.

There are many ways of carrying out a test for mould resistance.

1.  The Tantec method is to use a tropical chamber.  This is a cabinet designed to accelerate mould growth.  It is kept warm (25 to 30 Deg. C), and very moist.  Samples of mould bearing items (soil, cultures, leather) are placed into the chamber.  A gentle air flow is kept moving to spread mould spores continuously throughout the chamber.

Poorly treated leather will, in the chamber, have significant mould growth within a few weeks.  Well treated leather will be largely free of mould after this time.

Tantec includes control samples in the test.

•  Negative controls.  Pieces of wet blue with no fungicide
•  Borderline controls.  Pieces of wet blue treated with fungicide, but to a level barely adequate.
•  Positive controls.  Pieces of wet blue well treated with fungicide.

2.  A second test method often used, is to place leather samples onto a sterile disc on agar in a petri dish, and inoculate the agar with moulds.  The dish is incubated till mould is seen to grow over the leather.  Tantec does not use this method for three reasons.

• It tends to take much longer to get a result.
• It is too easy to manipulate results by carefully selecting which mould to inoculate the dish with.  Tantec prefers the ‘wild’ chamber which cannot be controlled.
• If this test is badly carried out, fungicides that can be washed out by water will end up in a thin zone around the sample, leaving a “zone of inhibition” that is mould-free.  This is a sign of failure (because fungicides should fix firmly to leather, and not wash out), but is often misrepresented as a sign of success.

An improved variation on the petri dish method which can be carried out by the tanner is to randomly ‘pre-inoculate’ the petri dish, by exposing it to the air inside the tannery for at least an hour.  Then the leather sample is added, and the incubation begins.  Doing this will remove the second objection above, and expose the leather to a random sampling of ‘local’ moulds. We at Tantec approve of this method, since it is not controlled, and gives a better reflection of local conditions.

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